YARN-1374. Changed ResourceManager to start the preemption policy monitors as active services. Contributed by Karthik Kambatla.
svn merge --ignore-ancestry -c 1539089 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1539090 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5458. Datanode failed volume threshold ignored if exception is thrown in getDataDirsFromURIs. Contributed by Mike Mellenthin.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1539092 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-HADOOP-9166-a-branch-2-gd