svn merge -c 1555161 FIXES: MAPREDUCE-5689. MRAppMaster does not preempt reducers when scheduled maps cannot be fulfilled. Contributed by Lohit Vijayarenu


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1574272 13f79535-47bb-0310-9956-ffa450edef68