RFR(M): 8132710, 8132712: Add tests which check that Humongous objects behave as expected after different types of GCs

[Kirill Zhaldybin]

Dear all,

Could you please review this fix for 8132710 and 8132712?

The test creates different types of object graphs with Object arrays as 
nodes (to make them humongous) and checks that after different types GCs 
(Young, Full etc) objects' graphs were handled correctly.

Full test's description is in README file 
(http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8132712/webrev.02/test/gc/g1/humongousObjects/objectGraphTest/README.html).

WebRev: http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8132712/webrev.02/

CR:
https://bugs.openjdk.java.net/browse/JDK-8132710
https://bugs.openjdk.java.net/browse/JDK-8132712

Thank you.

Regards, Kirill