HADOOP-9355. Abstract Symlink tests to use either FileContext or FileSystem (Andrew Wang via Colin Patrick McCabe)

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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@1496693 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-MAPREDUCE-4884-branch-2-gd