YARN-443. allow OS scheduling priority of NM to be different than the containers it launches (tgraves)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1454412 13f79535-47bb-0310-9956-ffa450edef68
svn merge -c 1452372 FIXES: MAPREDUCE-5043 Fetch failure processing can cause AM event queue to backup and eventually OOM Contributed by Jason Lowe



git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1454440 13f79535-47bb-0310-9956-ffa450edef68