YARN-24. Nodemanager fails to start if log aggregation enabled and namenode unavailable. (sandyr via tucu)

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HADOOP-9357. Fallback to default authority if not specified in FileContext. Contributed by Andrew Wang


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1461901 13f79535-47bb-0310-9956-ffa450edef68