RFR: Adjust SA to reflect recent changes on JVM side

[Zhengyu Gu]

Recently upstreamed additional CollectedHeap APIs are slightly different 
from the ones when SA was implemented. Adjusting SA code to match recent 
changes on JVM side.

http://cr.openjdk.java.net/~zgu/shenandoah/sh-sa-refactor/webrev.00/index.html


Test:

   tier3_gc_shenandoah and hotspot_serviceability (fastdebug and release)

Thanks,

-Zhengyu