8061715: gc/g1/TestShrinkAuxiliaryData15.java fails with java.lang.RuntimeException: heap decommit failed - after > before
Summary: added WhiteBox methods to count regions and exact aux data sizes
Reviewed-by: jwilhelm, brutisso

Reviewed-by: tschatzl, jwilhelm

8062957: Heap is not shrunk when deallocating under memory pressure
Summary: Added explicit -XX:-ExplicitGCInvokesConcurrent to invocations
Reviewed-by: brutisso, tschatzl

Summary: Check that native memory is returned to the system when decommiting memory within the heap with G1.
Reviewed-by: tschatzl, jwilhelm
Contributed-by: NAndrey Zakharov <andrey.x.zakharov@oracle.com>