RFR: 8041506 - The test gc/g1/TestHumongousShrinkHeap.java reports that memory is not de-committed

[Andrey Zakharov]

Hi.
To proper testing of free list sorting we need to defragment memory with 
small young and humongous objects
This is test scenario:
Make enough space for new objects to prevent it going old.
  - allocate bunch of small objects, and a bit of humongous
several times.

Free almost all of allocated stuff. Check that heap shrinks after GC.

webrev: http://cr.openjdk.java.net/~jwilhelm/8041506/webrev.02/
bug: https://bugs.openjdk.java.net/browse/JDK-8041506

Thanks.