YARN-568. Add support for work preserving preemption to the FairScheduler.
Contributed by Carlo Curino and Sandy Ryza


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1480837 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4810. several HDFS HA tests have timeouts that are too short. Contributed by Chris Nauroth


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1480842 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-7435-branch-2-gd