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

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20171120/webrev.01/

Important performance changes:

rev 10197 : [backport] Passive should opt-in the barriers, not opt-out
rev 10198 : [backport] Enable biased locking for Shenandoah by default

Barrier change was amended with two guards to make tests pass.

Testing: hotspot_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey