Merge -r 1433483:1433484 from trunk to branch-2. Fixes: YARN-335. Fair scheduler doesn't check whether rack needs containers before assigning to node. Contributed by Sandy Ryza.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433504 13f79535-47bb-0310-9956-ffa450edef68