ISPN-4626 Race condition in the LocalEntryRetriever between iterator() a...

...nd hasNext()

https://issues.jboss.org/browse/ISPN-4626
So here's what I've observed:
T1: iterator()
T2: iterate data container
T1: queue is empty (T2 still did not insert into it), isComplete is false (iteration has not finished)
T1: hasNext =false

It is difficult to reproduce this issue. Needs tracing on, a bit of artificial CPU saturation, invocationCount increase in the test, debug mode, but still, it happens in the CI