[sh/jdk8] Backport Shenandoah with large pages and small heap and test

[Zhengyu Gu]

I would like to backport following 2 patches to Shenandoah/jdk8u.


8268127: Shenandoah: Heap size may be too small for region to align to
          large page size
8268699: Shenandoah: Add test for JDK-8268127

JDK-8268127 also fixed minimum region count requirement.

Both patches don't apply cleanly.

JDK-8268127: Context is quite different, resolved manually.
JDK-8268699: Removed "@requires vm.gc.Shenandoah" annotations, that is
              not recognizable in 8u


Webrev:
http://cr.openjdk.java.net/~zgu/shenandoah/largepage_smallheap/webrev.00/

Test:
   hotspot_gc_shenandoah with new test.

Thanks,

-Zhengyu