YARN-1536. Cleanup: Get rid of ResourceManager#get*SecretManager() methods and use the RMContext methods instead. (Anubhav Dhoot via kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1580130 13f79535-47bb-0310-9956-ffa450edef68