Python code modernization, 3/n (#1157)

* Remove __metaclass__ = type.

for i in $(grep -REl '__metaclass__ = type' plugins/ tests/); do
  sed -e '/^__metaclass__ = type/d' -i $i;
done

* Remove super arguments, and stop inheriting from object.

plugins/modules/docker_image.py

@@ -433,7 +433,7 @@ class ImageManager(DockerBaseClass):
         :type results: dict
         """
 
-        super(ImageManager, self).__init__()
+        super().__init__()
 
         self.client = client
         self.results = results