MB-5195 use uuid for triggering significant_event on rebalance status

.. change. this will ensure that UI will see the rebalance result
even if rebalance dies too quick

Change-Id: I44a39760b720f54ade690982eebf9b2300feb369
Reviewed-on: http://review.couchbase.org/38217
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
undefine graceful_failover_pid config key on move_vbuckets action

so UI don't get confused if there was prior graceful failover

Change-Id: If7ca5820e13667603684bd74f60dd6f8350b9afd
Reviewed-on: http://review.couchbase.org/38218
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>