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
@pruivo That is a good point.  Though since I am using multiple threads, I think using an executor service would be a bit nicer.  I just saw that we have getTestThreadFactory, WDYT if I use that ?