svn merge -c 1445006 from trunk for HDFS-4342. Directories configured in dfs.namenode.edits.dir.required but not in dfs.namenode.edits.dir are silently ignored.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1445007 13f79535-47bb-0310-9956-ffa450edef68