Change ServoGraphiteSetup to ignore if a metric publisher already exists

Fixes this exception that I was gettting.

com.redhat.lightblue.rest.metadata.RestApplication threw exception: java.lang.IllegalStateException: Another strategy was already registered.
        at com.netflix.hystrix.strategy.HystrixPlugins.registerMetricsPublisher(HystrixPlugins.java:180)
        at com.redhat.lightblue.util.ServoGraphiteSetup.doInitialize(ServoGraphiteSetup.java:72)
        at com.redhat.lightblue.util.ServoGraphiteSetup.initialize(ServoGraphiteSetup.java:62)
        at com.redhat.lightblue.rest.metadata.MetadataResource.<clinit>(MetadataResource.java:31)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
        at org.jboss.resteasy.core.ConstructorInjectorImpl.construct(ConstructorInjectorImpl.java:82)
        at org.jboss.resteasy.plugins.server.resourcefactory.POJOResourceFactory.createResource(POJOResourceFactory.java:43)
        at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:215)
        at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:542)
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:524)
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:126)
        at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208)
        at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55)
        at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481)
        at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:145)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:336)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:653)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:508)
        at org.jboss.threads.SimpleDirectExecutor.execute(SimpleDirectExecutor.java:33)
        at org.jboss.threads.QueueExecutor.runTask(QueueExecutor.java:806)
        at org.jboss.threads.QueueExecutor.access$100(QueueExecutor.java:45)
        at org.jboss.threads.QueueExecutor$Worker.run(QueueExecutor.java:826)
        at java.lang.Thread.run(Thread.java:745)
        at org.jboss.threads.JBossThread.run(JBossThread.java:122)