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
the use of a CDL looks an attempt to run at the same time. but you are right, it is broken. 

```runConcurrently()``` looks good. maybe you can create a new method to run the same runnable N times?