HADOOP-10094. Merging change r1541991 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1541993 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5616. Merging change r1542001 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1542003 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5506. Merge change r1542011 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1542015 13f79535-47bb-0310-9956-ffa450edef68
Merging r1541995 from trunk to branch-2 for YARN-1222. Make improvements in ZKRMStateStore for fencing (Karthik Kambatla via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1542026 13f79535-47bb-0310-9956-ffa450edef68
YARN-1401. With zero sleep-delay-before-sigkill.ms, no signal is ever sent (Gera Shegalov via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1542047 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-YAHOO-286-branch-2-gd