RFR [8], 2018-06-13, Bulk backports to sh/jdk8

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20180613/webrev.01/

This backports recent bugfixes and performance improvements to sh/jdk8:

 [backport] Disable UseFastJNIAccessors for Shenandoah
 [backport] Should cleanup previous/bad versions of redefined classes during full gc
 [backport] Including metaspace info when reporting heap info
 [backport] Adaptive CSet selection selects excessively when memory is tight
 [backport] Parallel +AlwaysPreTouch should run with max workers
 [backport] Fix TestCommonGCLoads test
 [backport] Added logging for the number of workers used for GC cycles
 [backport] C1 shenandoah_wb expects obj in a register
 [backport] Some trivial-ish cleanups
 [backport] Replace ShBarrierSet* casts with accessor
 [backport] Perform gc-state checks with LoadB to fit C2 matchers

Testing: hotspot_tier3_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey