RFR [9]: Bulk backport to sh/jdk9

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk9-20171016/webrev.01/

This change backports most of the outstanding work to sh/jdk9. It is based on the patch that purges
partial and matrix code from 9, and this is why the webrev is relatively small.

Changes include:

rev 13688 : [backport] Remove ShenandoahGCWorkerPerJavaThread flag
rev 13689 : [backport] Double check for UseShenandoahGC in WB expand
rev 13690 : [backport] Verifier should print verification label at liveness verification
rev 13691 : [backport] Mark bitmap slices commit/uncommit + Aggregated bitmap slicing
rev 13692 : [backport] Fixed several string dedup bugs
rev 13693 : [backport] Fix (external) heap iteration + TestHeapDump should unlock aggressive heuristics
rev 13694 : [backport] Pauses that do not affect heap occupancy should not report heap
rev 13695 : [backport] Make sure -XX:+ShenandoahVerify comes first in the tests
rev 13696 : [backport] Add -XX:+ShenandoahVerify to more interesting tests
rev 13697 : [backport] Clean up dead code

I need sign-offs from everybody.

Testing: hotspot_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey