HDFS-6704. Merge r1612613 from trunk.

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HDFS-6701. Make seed optional in NetworkTopology#sortByDistance. Contributed by Ashwin Shankar.

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Merge r1612626 from trunk. YARN-2295. Refactored DistributedShell to use public APIs of protocol records. Contributed by Li Lu

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YARN-2131. Addendum2: Document -format-state-store. Add a way to format the RMStateStore. (Robert Kanter via kasha)

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