HBASE-8355: BaseRegionObserver#pre(Compact|Flush|Store)ScannerOpen returns null (Andrew Purtell, Jesse Yates)

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1483094 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8435 Test for zk leak does not account for unsynchronized access to zk watcher: ADDENDUM

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1483117 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-YAHOO-311-trunk-gd