MB-12249: Fix gc-couchbase tests

The tests now need the fake DCP server to start up.

Also the results can contain a geometry, currently it is set to
`nil` as the tests don't supply one.

Change-Id: I9d391feaebf965f05f706b6aa7c8e924da4fb666
Reviewed-on: http://review.couchbase.org/41768
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>