Enable acceptance tests again on Drone 0.7

Running the acceptance tests on Drone relied on the pod-style networking
used by services (service containers were available at 127.0.0.1 from
the build containers). However, in Drone 0.7 service and build
containers must be accessed from each other using their domain name
instead. Thus, acceptance tests had to be disabled on Drone.

Now that the acceptance test system supports setting a different domain
for the Selenium server and for the Nextcloud test server the acceptance
tests can be enabled again on Drone.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>