YARN-1033. Expose RM active/standby state to Web UI and REST API (kasha)

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HADOOP-10178. Merging change r1557236 from trunk to branch-2.

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HDFS-5756. hadoopRzOptionsSetByteBufferPool does not accept NULL argument, contrary to docs. Contributed by Colin Patrick McCabe.

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YARN-1574. RMDispatcher should be reset on transition to standby. (Xuan Gong via kasha)

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