HBASE-8787 Merged region endkey is incorrect if one region has null endkey

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1495746 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8750 MetaServerShutdownHandler stucks if .META. assignment fails in previous attempt

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1495747 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/0.95' into 0.95-gd