YARN-874. Making common RPC to switch to not switch to simple when other mechanisms are enabled and thus fix YARN/MR test failures after HADOOP-9421. Contributed by Daryn Sharp and Vinod Kumar Vavilapalli.
svn merge --ignore-ancestry -c 1496692 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1496694 13f79535-47bb-0310-9956-ffa450edef68