RFR: SA is broken during recent code reshuffling

[Zhengyu Gu]

There are two changes that break Shenandoah SA

- Upstream code reshuffling that moved GC vmStructs under gc/shared, 
Shenandoah vmStructs went missed during this change.

- Converted ShenandoahHeap::_regions from region set to region array, 
but SA was not updated.

Borrowed a SA test to make sure this won't happen again.

Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/sa-fix/webrev.00/


Test:

   hotspot_gc_shenandoah (release and fastdebug)


Thanks,

-Zhengyu