RFR(M): 8132718: Add tests which check that when humongous classloader object becomes unreachable it and all classes that were loaded in it should be collected

[Kirill Zhaldybin]

Dear all,

Could you please review this fix for JDK-8132718?

A new test added which creates non-humongous and humongous class 
loaders, loads the latter into the former, then loads 4 generated 
classes (both humongous and non-humongous) into humongous class loader.
After all generated classes are made unreachable and the test checks 
that all these classes are actually unloaded.

The testlibrary part is sent as fix for 8153764.


WebRev: http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8132718/webrev.05/

CR: https://bugs.openjdk.java.net/browse/JDK-8132718

Thank you.

Regards, Kirill