YARN-2615. Changed ClientToAMTokenIdentifier/RM(Timeline)DelegationTokenIdentifier to use protobuf as payload. Contributed by Junping Du
(cherry picked from commit ea26cc0b4ac02b8af686dfda80f540e5aa70c358)

Conflicts:
	hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/security/TestClientToAMTokens.java