RFR [8u] 2018-03-13: Bulk backports to sh/jdk8u

[Roman Kennke]

Looks good!
Thanks!

Roman

> http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20180313/webrev.01/
> 
> These backport last week's work to sh/jdk8u, plus a test timeout fix:
> 
> test-timeout: StringInternCleanup times out
> eac60de937c2: [backport] Excessive assert in ShHeap::mark_next
> b3446fc50093: [backport] Eliminate write-barrier assembly stub (part 1)
> 58279d273cc4: [backport] Degenerated GC: rename enum, report degen reasons in stats
> 0e32109905c8: [backport] Use os::naked_short_sleep instead of naked Thread events for sleeping
> 6d92c949ae62: [backport] No need for fence in control loop: flags are now ShSharedVariables
> 35f512e2f57f: [backport] Implement protocol for safe OOM during evacuation handling + Use jint in
> oom-evac-handler to match older JDKs Atomic support better + Missing OOMScope in ShenandoahFixRootsTask
> 125606c17be3: [backport] Minor cleanups
> 51fc1ad2dbff: [backport] Make control loop more responsive under allocation pressure
> 232c31483a6b: [backport] Split live data management for allocations and GCs
> 
> Testing: hotspot_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>