Rename checknewer to checknewer.py and fix Flake8 fallout

This is a python script so as the majority of scripts in here
it should end in a .py suffix

README.asciidoc

@@ -32,7 +32,7 @@ Scripts
 * *link:docs/maintbot.asciidoc[maintbot].* script that checks maintenance
   incidents to make sure the Factory maintainer submitted the package.
 
-* *link:checknewer[checknewer].* script compares version numbers in repos to
+* *link:checknewer.py[checknewer.py].* script compares version numbers in repos to
   make sure all packages e.g. in a new distro are newer
 
 Installation

checknewer.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 # Copyright (c) 2016 SUSE LLC
 #
 # Permission is hereby granted, free of charge, to any person obtaining a copy

tests/__init__.py

@@ -1,4 +1,3 @@
-#!/usr/bin/env python
 # -*- coding: utf-8 -*-
 #
 # (C) 2014 tchvatal@suse.cz, openSUSE.org