Make possible to set the expected status of the well known URL check

The check is based on the HTTP status returned by the URL, and different
URLs may return different status (for example, DAV returns 207, while
a service like WebFinger would return 200), so the expected status needs
to be set depending on the URL.

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