HDFS-6503. Merge r1601958 from trunk.

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HDFS-6315. Merge r1601960 from trunk.

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Merge r1601964 from trunk. YARN-2124. Fixed NPE in ProportionalCapacityPreemptionPolicy. Contributed by Wangda Tan

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Merge r1601980 from trunk. YARN-2125. Changed ProportionalCapacityPreemptionPolicy to log CSV in debug level. Contributed by Wangda Tan

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HADOOP-10656. Merging change r1601985 from trunk

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Merge HDFS-2006 HDFS XAttrs feature from Trunk to Branch-2

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