HDFS-4992. Make balancer's mover thread count and dispatcher thread count configurable.  Contributed by Max Lapan


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1503720 13f79535-47bb-0310-9956-ffa450edef68
Back out revision 1503499 for MAPREDUCE-5317. Stale files left behind for failed jobs


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1503744 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HDFS-4310-trunk-gd