Sometimes we synchronize on RegionState instance updating it, most of the time we don't. Fix

We synchronize on region state doing single assign of a region but then over in the handleRegion zk callback, we don't synchronize on the regionstate instance. Makes no sense. Either get rid of all synchronization or put synchronization everywhere (we should probably do the latter since it makes things easier to reason about, and these states are already complicated. There could be a performance issue though).