Stress test Support refactored

Refactored StressTestSupport, and fixed problems.

the kill thread was not being terminated correctly or waited on,  and in some cases the kill thread would be running, while we are doing our asserts.


AtomicLongGetAndAddStressTest  and AtomicLongUpdateStressTest,  do not seem to fail any more ?
I AtomicLongUpdateStressTest back, just to double check !