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
I would only lose it if was null in which case I know the value, if it was non null then it would be properly asserted.  Although I agree maybe a new method would be better.