RFR(S): 8132721: Add tests which check that heap counters work as expected during Humongous allocations

[Kirill Zhaldybin]

Dear all,

Could you please take a look at this test for JDK-8132721?

The test allocates/deallocates humongous objects and checks that memory 
counters (from Runtime and MemoryMXBean classes) work right.

For example it's expected that after allocating HO of size
(G1Region/2 + 1) bytes free memory should decrease on full G1Region
size.

CR:
https://bugs.openjdk.java.net/browse/JDK-8132721

WebRev:
http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8132721/webrev.04/


Thank you.
Regards, Kirill