[infinispan-dev] [ISPN-731] - make rehashing state and tx log draining serial

Mircea and I concluded that it is worth keeping the current pull state approach and bolting proper tx log draining unless this solution becomes more complex than the original push state approach that already serialized state sending and tx log draining. To summarize, during leave rehash, we need state senders to drain tx log (InvertedLeaveTask#processAndDrainTxLog) *after* all state receivers have transferred the state. As things stand right now (InvertedLeaveTask#performRehash) tx log draining is interleaved with state transfer leading to problems described in the above mentioned JIRA. The solution I have in mind is to introduce a Map<Integer,CountDownLatch> in DistributedManagerImpl. They keys in this map will be view ids for the leave rehash while CountDownLatch will be initialized to the number of state receivers. As state receivers pick up state we countDown on the latch. State provider awaits on a latch for a given view id and a timeout. When await returns it drains the tx log. Let me know what you think. Regards, Vladimir