HBASE-8493 Backport HBASE-8422, 'Master won't go down', to 0.94 (rajeshbabu)

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1483045 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8540 SnapshotFileCache logs too many times if snapshot dir doesn't exists

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1483046 13f79535-47bb-0310-9956-ffa450edef68