RFR [11]: 2018-10-29, Bulk backports to sh/jdk11

[Roman Kennke]

Looks good. Thanks!

Roman

> http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20181029/webrev.01/
> 
> Small batch of outstanding work from last week:
> 
>  [backport] revert some useless C2 changes
>  [backport] JVMTI lacks a few GC barriers/hooks
>  [backport] Cherry-pick JDK-8212673, fix for Node::eqv_uncast
>  [backport] Clean up ShHeap::heap_region_iterate uses
>  [backport] Parallel heap region iteration
>  [backport] Parallelise "Clear Liveness"
>  [backport] Parallelise "Complete Liveness"
> 
> Testing: tier3_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>