HDFS-6105. Merge r1579468 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1579474 13f79535-47bb-0310-9956-ffa450edef68
YARN-1640. Fixed manual failover of ResourceManagers to work correctly in secure clusters. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1579510 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1579511 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-2349. Modified FileInputFormat to be able to issue file and block location calls in parallel. Contributed by Siddharth Seth.
svn merge --ignore-ancestry -c 1579515 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1579516 13f79535-47bb-0310-9956-ffa450edef68