YARN-2635. TestRM, TestRMRestart, TestClientToAMTokens should run with both CS and FS. (Wei Yan and kasha via kasha)

(cherry picked from commit 80d11eb68e60f88e16d7d41edecbddfc935a6b10)

Conflicts:
	hadoop-yarn-project/CHANGES.txt
	hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/security/TestClientToAMTokens.java
YARN-2635. Merging to branch-2.6 for hadoop-2.6.0-rc1.

(cherry picked from commit 81dc0ac6dcf2f34ad607da815ea0144f178691a9)

Conflicts:
	hadoop-yarn-project/CHANGES.txt
YARN-2853. Fixed a bug in ResourceManager causing apps to hang when the user kill request races with ApplicationMaster finish. Contributed by Jian He.

(cherry picked from commit 3651fe1b089851b38be351c00a9899817166bf3e)

Conflicts:
	hadoop-yarn-project/CHANGES.txt
YARN-2853. Merging to branch-2.6 for hadoop-2.6.0-rc1.

(cherry picked from commit d648e60ebab7f1942dba92e9cd2cb62b8d70419b)

Conflicts:
	hadoop-yarn-project/CHANGES.txt
YARN-1964. Adding changelog back in.