[8] RFR: 2020-02-07, Bulk backports to sh/jdk8

[Aleksey Shipilev]

https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20200207/

Some changes required quite a bit of adaptation, so please review carefully.

List of changes:
 [backport] 8227327: Shenandoah: Faster and more parallel tests
 [backport] 8237570: Shenandoah: cleanup uses of allocation/free threshold in static heuristics
 [backport] 8237586: Shenandoah: provide option to disable periodic GC
 [backport] 8237038: Shenandoah: Reduce thread pool size in TestEvilSyncBug.java test
 [backport] 8233850: Shenandoah: Shenandoah thread count ergonomics should be container aware
 [backport] 8236851: Shenandoah: More details in Traversal GC event messages
 [backport] 8236106: [TESTBUG] Shenandoah: Make TestThreadFailure more resilient
 [backport] 8235729: Shenandoah: Remove useless casting to non-constant
 [backport] 8233520: Shenandoah: do not sleep when thread is attaching
 [backport] 8233387: Shenandoah: passive mode should disable pacing ergonomically

Testing: x86_64, hotspot_gc_shenandoah, fastdebug/release

-- 
Thanks,
-Aleksey