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/module_utils/_util.py

@@ -121,7 +121,7 @@ def log_debug(msg, pretty_print=False):
             log_file.write(f"{msg}\n")
 
 
-class DockerBaseClass(object):
+class DockerBaseClass:
     def __init__(self):
         self.debug = False
 
@@ -245,7 +245,7 @@ def compare_generic(a, b, method, datatype):
         return True
 
 
-class DifferenceTracker(object):
+class DifferenceTracker:
     def __init__(self):
         self._diff = []