HADOOP-10678. Merging change r1602473 from trunk to branch-2.

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HDFS-6330. Merge r1602484 from trunk.

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HDFS-6470. TestBPOfferService.testBPInitErrorHandling is flaky. Contributed by Ming Ma.

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HADOOP-10688. Expose thread-level FileSystem StatisticsData (Sandy Ryza)

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