HADOOP-10872: Merging r1612895 from trunk to branch-2.

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HADOOP-10830. Missing lock in JavaKeyStoreProvider.createCredentialEntry. Contributed by Benoy Antony.

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Moved CHANGES.txt entry for HADOOP-10830 to 2.6 section

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HADOOP-10890: Merging r1612916 from trunk to branch-2.

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Merge from trunk. HDFS-6422. getfattr in CLI doesn't throw exception or return non-0 return code when xattr doesn't exist. (Charles Lamb via umamahesh)

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HDFS-6114. Block Scan log rolling will never happen if blocks written continuously leading to huge size of dncp_block_verification.log.curr (vinayakumarb via cmccabe)

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