DATAREDIS-299 - Assert compatibility with Spring IO.

Upgrade to JUnit 4.11

Upgrade to JUnit 4.11 and remove use of a matcher in an internal
package in favour of the Hamcrest equivalent. To avoid a clash between
JUnit 4.11's Hamcrest dependency and the version of Hamcrest that's
bundled in mockito-all, use of mockito-all has been replaced with
mockito-core.

Fixed deprecation warnings caused by Junit upgrade.

Add and configure the Spring IO plugin such that it's only applied when the
build is run with -PplatformVersion=<version>. This platformVersion
property is used to determine the version of the Platform that will
be used when running the springIoCheck task. The plugin can be used
by running a build as follows:

./gradlew clean springIoCheck -PplatformVersion=1.0.0.BUILD-SNAPSHOT -PJDK7_HOME=… -PJDK8_HOME=…

This will test the project on JDK7 and JDK 8 using the dependencies
defined in the latest snapshot of Spring IO Platform 1.0.0.