MB-17515: improve warning message
MB-17515: improve warning message

Along the lines suggested in the bug.

Change-Id: Id09b28f8c8d989f58f4f31b6950d120e0b6d7d47
Reviewed-on: http://review.couchbase.org/59694
Tested-by: Dave Finlay <7b10a9ed9f70e64c30b07607a671ae61c33f14c8@couchbase.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

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