RFR: Consistenly order STS scope outside of OOM scope to avoid deadlocks

[Roman Kennke]

We have observed very spurious deadlocks that involve the OOMEvacScope
and STSJoiner scope. It goes like this: Thread 1 enters OOM scope, but
did not yet enter the STS scope. Thread2 is inside both scopes and
OOM-s, cancelling evac and leaves the STS and attempts to leave the
OOM-scope, waiting for Thread 1. Apparently, another thread calls for a
(non-GC) safepoint, which makes Thread 1 block upon entering the STS
scope, in other words it will never leave the OOM scope.

Ordering the STS-scope consistently outside of OOM-scope should solve
this problem: the OOM-leaver will not get blocked by threads trying to
get into STS first, and will thus always leave all relevant scopes.

Testing: tier3_gc_shenandoah

http://cr.openjdk.java.net/~rkennke/sts-oom-deadlock/webrev.00/

Good?

Roman