Add option to acceptance test runner to set the Nextcloud server domain

By default "127.0.0.1" is used, so nothing needs to be set when the
Selenium server and the Nextcloud test server share the same network
(like when called by "run.sh").

Besides passing the domain to the acceptance tests the Nextcloud test
server configuration must be modified to see the given domain as a
trusted domain; otherwise the access would be forbidden.

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