MB-9343 add constants for UPR commands

Change-Id: I16495249c224fbb842874e7e0d0331267843c2f6
Reviewed-on: http://review.couchbase.org/32531
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>