Factor out a function to update rebalance status.
Factor out a function to update rebalance status.

Change-Id: Id4bfed4269036ba0c50ce8ba1d92df7e536da61c
Reviewed-on: http://review.couchbase.org/73533
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

membase/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,ceejatec/ns_server