ISPN-2581 StateTransferManagerImpl.waitForInitialStateTransferToComplete...

...() returns too soon

https://issues.jboss.org/browse/ISPN-2581

Should also resolve https://issues.jboss.org/browse/ISPN-2541

Don't flag the initial state transfer as complete as soon as we send the
rebalance confirmation to the coordinator. It will be flagged while
processing the next topology update.