RFR: Upstream JDK11 merge

[Roman Kennke]

This merges from jdk/jdk11 to shenandoah/jdk11 and pulls in up to tags
jdk-11+26 and jdk-11+27 and adds corresponding shenandoah-jdk-11+26 and
shenandoah-jdk-11+27 tags. No conficts (only .hgtags) and nothing
surprising coming in.

List of stuff:
http://cr.openjdk.java.net/~rkennke/upstream-jdk11-merge-2018-08-22/outgoing.txt

Testing: tier3_gc_shenandoah (ongoing, must be clean before push)

Ok?

Roman