HBASE-9539 Handle post namespace snapshot files when checking for HFile V1

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.96@1523868 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9554 TestOfflineMetaRebuildOverlap#testMetaRebuildOverlapFail fails due to NPE

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.96@1523869 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9467 write can be totally blocked temporarily by a write-heavy region

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.96@1523880 13f79535-47bb-0310-9956-ffa450edef68