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
True, but then we would lose the visibilty of the test assertion message if they didn't match.  I could move the assert inside the method maybe, but that seems uglier and more lines of code.  WDYT?