swh.lister.cgit: Remove repo page visit step

Remove the need to visit every page and extract the
origin url by introducing a parameter url_prefix.
The origin url is in format <prefix>/<repo_name> where
The prefix is same for all the repos for a particular
cgit instance.

swh/lister/cli.py

@@ -129,7 +129,8 @@ def cli(ctx, db_url, listers, drop_tables):
             from .cgit.models import ModelBase
             from .cgit.lister import CGitLister
             _lister = CGitLister(
-                      base_url='http://git.savannah.gnu.org/cgit/',
+                      url='http://git.savannah.gnu.org/cgit/',
+                      url_prefix='http://git.savannah.gnu.org/git/',
                       override_config=override_conf)
 
         else: