Statemachine for bookkeeper client

JIRA: https://issues.apache.org/jira/browse/BOOKKEEPER-723

Reporter: Sijie Guo @sijie

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FPJ: Just to be on the same page, even if we have a state machine for each component, they need to be interconnected somehow, since they are part of the same client and the behavior of one component influences the other, e.g., PCBC is not independent of BookieClient. Consequently, there should be implicit one state machine driving the whole computation of the client. An example of an overarching state machine like this is the ZK one for sessions:

http://zookeeper.apache.org/doc/r3.4.5/zookeeperProgrammers.html#ch_zkSessions
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