RFR [8]: 2018-10-05, Bulk backports to sh/jdk8u

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20181005/webrev.01/

This backports recent work to sh/jdk8u:

 [backport] Make Shenandoah to use ShenandoahOWST only
 [backport] Missed VerifyObjectEquals in VerifyJCStressTest
 [backport] Make sure debug builds fail predictably on safepoint timeout
 [backport] Beef up and parallelize EvilSyncBug test
 [backport] Enable string deduplication in all marking phases
 [backport] Precleaning should use GC workers to do actual work
 [backport] Fix compilation errors due to missing spaces between string literal and macro
 [backport] Remove dead-weight ShenandoahPrinter
 [backport] Rehash and cleanup usages of ShenandoahHeap::heap()
 [backport] Cleanup up superfluous newlines
 [backport] Cleanup C2 debugging leftovers

I had to do a few additional things in string dedup, because 8u code expects to pass
ShStrDedupQueues where needed.

Testing: hotspot_tier3_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey