Rearrange the imports to meet the style guide

This also includes `from __future__ import absolute_import`
in every file so that the imports are consistent in Python 2 and 3.
The Python 2 tests fail without this.

tests/test_common/test_messaging.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # SPDX-License-Identifier: MIT
+from __future__ import absolute_import
 
 from module_build_service.common import messaging
 from module_build_service.scheduler.parser import FedmsgMessageParser