Merge r1490470 from trunk to branch-2 for YARN-759. Create Command enum in AllocateResponse (bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490473 13f79535-47bb-0310-9956-ffa450edef68
svn merge -c 1490486 Merging from trunk to branch-2 to fix HDFS-4862.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490487 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd