RFR [8], 2018-07-30, Bulk backports to sh/jdk8

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20180730/webrev.01/

This backports latest work to sh/jdk8:

 [backport] Trace and report total allocation latency and sizes
 [backport] -XX:-UseTLAB should disable GCLABs too
 [backport] Refactoring ShenandoahStrDedupStress test to reduce test time
 [backport] Traversal should resize TLABs
 [backport] Refactor to group marking bitmap and TAMS structure in one class ShenandoahMarkingContext
 [backport] Refactor alive-closures to deal better with new marking contexts
 [backport] Avoid indirection to next-mark-context
 [backport] TLAB sizing policy should converge faster with Shenandoah
 [backport] Move periodic GC decision making to GC heuristics base class
 [backport] Handle missing ShenandoahWriteBarrierRB case
 [backport] Move Shenandoah stress tests to tier3

Testing: hotspot_tier3_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey