[11u]: 8048556: Unnecessary GCLocker-initiated young GCs

[Roman Kennke]

I'd like to backport the change to 11u.

Original bug:
https://bugs.openjdk.java.net/browse/JDK-8048556

Original change:
https://hg.openjdk.java.net/jdk/jdk/rev/8d3886985964

11u backport:
http://cr.openjdk.java.net/~rkennke/JDK-8048556/webrev-11.00/

Differences to original change are:
- Renamed files (e.g. vmGCOperations vs. gcVMOperations)
- In g1CollectedHeap.cpp, instead of "return false" only "return"
because that method is void in 11u. Functionally it should be equivalent.

The supplied testcase fails without the patch, and passes with the
patch. tier1 and tier2 are looking good here, without regressions.

Can I please get a review?

Thanks,
Roman