RFR [8], 2018-09-10, Bulk backports to sh/jdk8

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20180910/webrev.01/

This backports recent work to sh/jdk8:

 [backport] Allocation path should not touch GC barriers for metadata
 [backport] Soft refs should be purged reliably on allocation failure, or with compact heuristics
 [backport] shenandoah_assert_correct should verify classes before claiming _safe_oop
 [backport] Tests should use -XX:+ShenandoahVerify in some OOM-evac configurations
 [backport] Degenerated evacuation
 [backport] Soft-refs policy needs reliable heap usage data after the GC cycle
 [backport] Unreachable assert in ShenandoahCodeRoots::acquire_lock
 [backport] Prune undefined and unused methods
 [backport] Passive heuristics should enter degen GC, not full GC
 [backport] Reshuffle tests: verify STW GC is working first, then verify under aggressive, then the rest
 [backport] TestHeapDump runs much faster with small heap
 [backport] Cleanup: remove unused root processor's sub tasks
 [backport] EvilSyncBug test is too slow
 [backport] Purge partial heuristics and connection matrix infrastructure
 [backport] Remove NMethodSizeLimit adjustment for Shenandoah

Testing: hotspot_tier3_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey