HDFS-4359. Slow RPC responses from NN can prevent metrics collection on DNs. Contributed by liang xie.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1435300 13f79535-47bb-0310-9956-ffa450edef68
merge MAPREDUCE-4948 from trunk. Fix a failing unit test - TestYARNRunner.testHistoryServerToken. Contributed by Junping Du


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1435313 13f79535-47bb-0310-9956-ffa450edef68