[aarch64-port-dev ] RFR: Import 3 Shenandoah fixes into JDK8 integration repo

[Roman Kennke]

We need 3 more fixes from Shenandoah's JDK8u repo in the
aarch64/shenandoah integration repo:

http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/516125718f54
http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/335eb870833a
http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/b733ce321ce9


This is the combined changeset:

http://cr.openjdk.java.net/~rkennke/2017-04-20/webrev.00/

Ok to push?

Roman