HBASE-9843 Various fixes in client code

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.96@1536871 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9750 Add retries around Action server stop/start

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HBASE-9221: Provide interface for getting a User in the client

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HBASE-9221: Provide interface for getting a User in the client: ADDENDUM

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