MAPREDUCE-6002. Made MR task avoid reporting error to AM when the task process is shutting down. Contributed by Wangda Tan.
svn merge --ignore-ancestry -c 1613743 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1613744 13f79535-47bb-0310-9956-ffa450edef68