Add new option cacerts.

This way you can override the CAs, that are used for http communication.

tools/fast_puller_.py

@@ -44,9 +44,18 @@
 parser.add_argument('--directory', action='store',
                     help='Where to save the image\'s files.')
 
+parser.add_argument('--cacerts', help='A file, which contains all certs to use')
+
 _THREADS = 8
 
 
+def _apply_ca_certs(callable, ca_certs):
+  """Apply ca_certs attribute to default transport"""
+  def _call_with_a_certs(*args, **kwargs):
+    return callable(*args, ca_certs = ca_certs, **kwargs)
+  return _call_with_a_certs
+
+
 def main():
   logging_setup.DefineCommandLineArgs(parser)
   args = parser.parse_args()
@@ -55,6 +64,11 @@ def main():
   if not args.name or not args.directory:
     raise Exception('--name and --directory are required arguments.')
 
+  if args.cacerts:
+    logging.info('Adding CA certificates of %s', args.cacerts)
+    retry_transport.DEFAULT_SOURCE_TRANSPORT_CALLABLE = _apply_ca_certs(
+      retry_transport.DEFAULT_SOURCE_TRANSPORT_CALLABLE, args.cacerts)
+
   retry_transport_factory = retry_transport.Factory()
   transport = transport_pool.Http(retry_transport_factory.Build, size=_THREADS)