YARN-1417. Modified RM to generate container-tokens not at creation time, but at allocation time so as to prevent RM
from shelling out containers with expired tokens. Contributed by Omkar Vinit Joshi and Jian He.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1568060 13f79535-47bb-0310-9956-ffa450edef68