HDFS-6412. Interface audience and stability annotations missing from several new classes related to xattrs. (wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2006@1595099 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6410. DFSClient unwraps AclException in xattr methods, but those methods cannot throw AclException. (wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2006@1595101 13f79535-47bb-0310-9956-ffa450edef68