Decouple vbucket state change from updater

When partition state changes, view engine stops the updater and then update the partition state and then restart the updater.
If updater is in waiting queue, stop updater will block till updater moves to running state. This will unnecessarily block the movement of partition.

The updater can be removed from the waiting list when stop_updater is called and partition state can be updated and restart the updater. This will unblock partition state change call.