merge MAPREDUCE-4671 from trunk. AM does not tell the RM about container requests which are no longer needed. Contributed by Bikas Saha.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1443324 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'branch-2' of github.com:griddynamics/yhadoop-common into branch-2-gd
Merge branch 'branch-2-gd' of github.com:griddynamics/yhadoop-common into fb-YAHOO-225-branch-2-gd