HDFS-4659. Merge 1492914 from branch-2

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Merge -c 1492958 from trunk to branch-2.1-beta to fix YARN-812. Set default logger for application summary logger to hadoop.root.logger. Contributed by Siddarth Seth.

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svn merge -c 1492941 from trunk for HDFS-4845. FSNamesystem.deleteInternal should acquire write-lock before changing the inode map.


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Merge -c 1492962 from trunk to branch-2.1-beta to fix MAPREDUCE-5319. Set user.name in job.xml. Contributed by Xuan Gong.

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