RFR [10], 2018-04-18, Bulk backports to sh/jdk10

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk10-20180419/webrev.01/

This backports recent work to sh/jdk10:

 [backport] Only report GC pause time to GC MXBean + Re-fix memory managers and memory pools usage
and pause reporting
 [backport] Add test to verify Shenandoah is not enabled by default, and enabled with the flag
 [backport] Conditionalize x86 storeval barrier better
 [backport] Basic support for x86_32: build and run in STW configuration
 [backport] Bitmap based ShHeapRegionSet

Testing: hotspot_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey