RFR: [8u] Bulk backports to sh/jdk8u

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20180116/webrev.01/

This backports all outstanding work to sh/jdk8u. This passes a few nightlies in sh/jdk10. Some
changes, notably moving the VM operations around required some fiddling to match the code in sh/jdk8u.

Changes include:

 [backport] Increase test timeouts
 [backport] Report fwdptr size in JNI GetObjectSize
 [backport] Disable verification from non-Shenandoah VMOps.
 [backport] Cleanup reset_{next|complete}_mark_bitmap
 [backport] Verifier should check klass pointers before attempting to reach for object size
 [backport] TestSelectiveBarrierFlags times out due to too aggressive compilation mode
 [backport] Shenandoah SA implementation
 [backport] Allow use of fp spills around write barrier
 [backport] Rehash VMOperations and cycle driver mechanics for consistency
 [backport] Minor cleanup, uses latest Atomic API
 [backport] Match barrier fastpath checks better
 [backport] ShenandoahWriteBarrierRB flag to conditionally disable RB on WB fastpath

NIO checkIndex fix, and assorted Windows compilation fixes were already
backported by Zhengyu and Roman.

Testing: hotspot_gc_shenandoah {fastdebug|release}, some benchmarks

Thanks,
-Aleksey