Test that case for NonBlockingHashMapLong on putIfAbsent atomicity

This is a test case created to reproduce `NonBlockingHashMapLong#putIfAbsent()` atomicity issue reported as https://github.com/stephenc/high-scale-lib/issues/5.
Current version of `water.nbhm.NonBlockingHashMapLong` class passes both tests unlike SF version (i.e. (NonBlockingHashMapLong#putIfAbsent())) and it's clones.