cgit: reduce the batch size to 10 and add a bit of logging

Since the CGit lister now perform an HTTP query for each git repos listed in
the main index, it is significantly slower, so reducing the time between
database commits make sense, and won't overload the database.

With a bit of logging, it makes it easier to follow/debug the progress of
a listing.

swh/lister/cgit/lister.py

@@ -3,6 +3,7 @@
 # See top-level LICENSE file for more information
 
 import re
+import logging
 from urllib.parse import urlparse, urljoin
 
 from bs4 import BeautifulSoup
@@ -15,6 +16,9 @@ from swh.core.utils import grouper
 from swh.lister.core.lister_base import ListerBase
 
 
+logger = logging.getLogger(__name__)
+
+
 class CGitLister(ListerBase):
     """Lister class for CGit repositories.
 
@@ -70,12 +74,15 @@ class CGitLister(ListerBase):
         self.session.mount(self.url, HTTPAdapter(max_retries=3))
 
     def run(self):
-        for repos in grouper(self.get_repos(), 100):
+        total = 0
+        for repos in grouper(self.get_repos(), 10):
             models = list(filter(None, (self.build_model(repo)
                                         for repo in repos)))
             injected_repos = self.inject_repo_data_into_db(models)
             self.schedule_missing_tasks(models, injected_repos)
             self.db_session.commit()
+            total += len(injected_repos)
+            logger.debug('Scheduled %s tasks for %s', total, self.url)
 
     def get_repos(self):
         """Generate git 'project' URLs found on the current CGit server