Add helper make file.

Mainly to regenerate protocol.pb.go when protocol.proto gets updated.

Change-Id: I50bdd767bdbc4b72fc144b935db9208b55651af1
Reviewed-on: http://review.couchbase.org/42849
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>