RFR: Bulk backport to sh/jdk8u

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20170927/webrev.01/

Includes:

rev 10119 : [backport] Verify regions status
rev 10120 : [backport] Asynchronous region recycling
rev 10121 : [backport] Heap region sampling should publish region states
rev 10122 : [backport] Store checks should run most of the time
rev 10123 : [backport] FreeSet refactor: bitmaps, cursors, biasing
rev 10124 : [backport] Trim the TLAB sizes to avoid wasteful retirement under TLAB races
rev 10125 : [backport] Adaptive collection set selection in adaptive policy
rev 10126 : [backport] Make heap counters update completely asynchronous
rev 10127 : [backport] Adaptive heuristics accounts trashed cset twice

Testing: hotspot_gc_shenandoah

(There are some interesting test timeouts that are present even with current 8u, trying to resolve
them separately)

Thanks,
-Aleksey