ISPN-3367 ClusterTopologyManagerTest.testClusterRecoveryWithRebalance fails randomly

Lower MERGE2.max_interval to speed up merging.
ISPN-3965 Tests in org.infinispan.server.test.client.hotrod can fail due to NPE
ISPN-3964 Move unstable tests to different group

* No tests are disabled. Unstable (random failing) tests should be
marked with group 'unstable'.  This can be applied to a class or
a method.
* Added profile test-unstable (-Ptest-unstable) to run only the
'unstable' group.
* Enabled all stress,profiling,manual tests since they do not run
automatically.
* Removed not implemented tests.
Infinispan requires JDK 7 for building