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

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1483095 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8435 Test for zk leak does not account for unsynchronized access to zk watcher: ADDENDUM

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