HDFS-5078. Merging change r1518292 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1518813 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5441. Changed MR AM to return RUNNING state if exiting when RM commands to reboot, so that client can continue to track the overall job. Contributed by Jian He.
svn merge --ignore-ancestry -c 1518821 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1518824 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9889. Refresh the Krb5 configuration when creating a new kdc in Hadoop-MiniKDC (Wei Yan via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1518849 13f79535-47bb-0310-9956-ffa450edef68