message: HTTPDownload: Improve error message.
diff: @@ -4154,7 +4154,10 @@ class HTTPDownload(Builder):
  if response.status == 200:
  break
  if response is None:
  - raise Exception('Unable to download %s' % self.__urls)
  + raise Exception(
  + 'Unable to download {}'.format(
  + pretty_listing(
  + self.__urls, any = True, quantifier = True))
  return response.status, response.read()
  status, content = self._run_job(job)
  if status != 200:
  