ISPN-4521 ReplicationQueueTest.testReplicationQueueMultipleThreads

random failures

* Updated test to use proper assertions
* Changed test to use eventually
* Changed test threading to use thread pool

https://issues.jboss.org/browse/ISPN-4521
And actually looking at runConcurrently in AbstractInfinispanTest, that is broken for the same reason.  Although the method is unused, guess I should fix that one as well.