YARN-2977. Fixed intermittent TestNMClient failure. (Contributed by Junping Du)

(cherry picked from commit cf7fe583d14ebb16fc1b6e29dc2afbf67d24b9d1)
CHANGES.txt: add YARN-2977

(cherry picked from commit 76b0370a27c482caff9498e15ef889d37f413ce7)

Conflicts:
	hadoop-yarn-project/CHANGES.txt
Revert "YARN-2977. Fixed intermittent TestNMClient failure. (Contributed by Junping Du)"

This reverts commit d79f63120e16cb03f3f85b5d79a84202881a95a5.
Revert "CHANGES.txt: add YARN-2977"

This reverts commit 3419091631777ec04dd1a9e2bf24adab2496c5ce.