Add isort and flake8 to CI (#869)

* Run isort.

* Clean up unused assignments.

* Add flake8 linting step.

plugins/module_utils/_version.py

@@ -27,11 +27,14 @@ Every version number class implements the following interface:
     of the same class, thus must follow the same rules)
 """
 
-from __future__ import (absolute_import, division, print_function)
+from __future__ import absolute_import, division, print_function
+
+
 __metaclass__ = type
 
 import re
 
+
 try:
     RE_FLAGS = re.VERBOSE | re.ASCII
 except AttributeError: