Add the Spring IO Platform plugin

With thanks to the pointers from Artem, the `spring-integration-jpa` and `spring-integration-gemfire` tests now pass when run with the Spring IO versions: note the changes to apply the javaagents and forkEvery to every Test task. However, I'm seeing failures in `spring-integration-core` and `spring-integration-twitter` due to a `MalformedParameterizedTypeException`. Given that it's using a snapshot, I'm not sure that you'll want to merge this PR yet, but I thought it would be a reasonable way to share what I've done and discuss the test failures.

In both cases the failures seem to be related to retry advice. I _think_ these failures are legitimate problems, rather than due to the plugin. You can reproduce the failure by running `/gradlew springioCheck -PJDK7_HOME=/Library/Java/JavaVirtualMachines/jdk7/Contents/Home/` (updating JDK7_HOME as appropriate for your OS). You should see a single failure in `spring-integration-core`:

```
org.springframework.integration.config.xml.RetryAdviceParserTests > testAll:

java.lang.IllegalStateException: Failed to load ApplicationContext
	at org.springframework.test.context.CacheAwareContextLoaderDelegate.loadContext(CacheAwareContextLoaderDelegate.java:99)
	at org.springframework.test.context.DefaultTestContext.getApplicationContext(DefaultTestContext.java:101)
	at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:109)
	at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:75)
	at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:324)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:213)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:290)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:292)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:233)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:87)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:176)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.runTestClass(JUnitTestClassExecuter.java:86)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.execute(JUnitTestClassExecuter.java:49)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassProcessor.processTestClass(JUnitTestClassProcessor.java:69)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:50)
	at sun.reflect.GeneratedMethodAccessor18.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.messaging.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
	at org.gradle.messaging.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
	at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:103)
	at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.messaging.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:355)
	at org.gradle.internal.concurrent.DefaultExecutorFactory$StoppableExecutorImpl$1.run(DefaultExecutorFactory.java:64)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:744)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'a1': Initialization of bean failed; nested exception is java.lang.reflect.MalformedParameterizedTypeException
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:547)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:703)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
	at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:125)
	at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:60)
	at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.delegateLoading(AbstractDelegatingSmartContextLoader.java:100)
	at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.loadContext(AbstractDelegatingSmartContextLoader.java:250)
	at org.springframework.test.context.CacheAwareContextLoaderDelegate.loadContextInternal(CacheAwareContextLoaderDelegate.java:64)
	at org.springframework.test.context.CacheAwareContextLoaderDelegate.loadContext(CacheAwareContextLoaderDelegate.java:91)
	... 42 more
Caused by: java.lang.reflect.MalformedParameterizedTypeException
	at sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl.validateConstructorArguments(ParameterizedTypeImpl.java:60)
	at sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl.<init>(ParameterizedTypeImpl.java:53)
	at sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl.make(ParameterizedTypeImpl.java:95)
	at sun.reflect.generics.factory.CoreReflectionFactory.makeParameterizedType(CoreReflectionFactory.java:105)
	at sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:140)
	at sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49)
	at sun.reflect.generics.repository.ConstructorRepository.getParameterTypes(ConstructorRepository.java:94)
	at java.lang.reflect.Method.getGenericParameterTypes(Method.java:292)
	at java.beans.FeatureDescriptor.getParameterTypes(FeatureDescriptor.java:387)
	at java.beans.MethodDescriptor.setMethod(MethodDescriptor.java:114)
	at java.beans.MethodDescriptor.<init>(MethodDescriptor.java:72)
	at java.beans.MethodDescriptor.<init>(MethodDescriptor.java:56)
	at java.beans.Introspector.getTargetMethodInfo(Introspector.java:1149)
	at java.beans.Introspector.getBeanInfo(Introspector.java:416)
	at java.beans.Introspector.getBeanInfo(Introspector.java:163)
	at org.springframework.beans.CachedIntrospectionResults.<init>(CachedIntrospectionResults.java:284)
	at org.springframework.beans.CachedIntrospectionResults.forClass(CachedIntrospectionResults.java:188)
	at org.springframework.beans.BeanWrapperImpl.getCachedIntrospectionResults(BeanWrapperImpl.java:327)
	at org.springframework.beans.BeanWrapperImpl.getPropertyDescriptors(BeanWrapperImpl.java:335)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.filterPropertyDescriptorsForDependencyCheck(AbstractAutowireCapableBeanFactory.java:1343)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.filterPropertyDescriptorsForDependencyCheck(AbstractAutowireCapableBeanFactory.java:1322)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1180)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
	... 56 more
```

I've you run with `--continue` you'll also see very similar failures in `spring-integration-twitter`.

If you'd like to see the versions of the dependencies that the tests are being run against use `./gradlew ./gradlew spring-integration-core:dependencies --configuration springioTestRuntime`

Please let me know if there's anything I can do to help