Lint this entire monstrosity

- Doing some of @schoen's refactoring homework for him :)

letsencrypt/plugins/manual.py

@@ -93,7 +93,6 @@ s.serve_forever()" """
     def prepare(self):  # pylint: disable=missing-docstring,no-self-use
         if self.config.noninteractive_mode:
             raise errors.PluginError("Running manual mode non-interactively is not supported")
-        pass  # pragma: no cover
 
     def more_info(self):  # pylint: disable=missing-docstring,no-self-use
         return ("This plugin requires user's manual intervention in setting "