MB-18318 Expect missing rebalance timestamp.
MB-18318 Expect missing rebalance timestamp.

That can happen if node is added to the cluster and then immediately
ejected (it's not even possible to do this using our UI). In that
case, since service_map is unchanged, there will be no rebalance
timestamp.

Change-Id: I4a34a2991697ad1a48da8b8fb5e08804371f9cfa
Reviewed-on: http://review.couchbase.org/60435
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

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