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.

.pylintrc

@@ -406,7 +406,6 @@ disable=raw-checker-failed,
         redefined-outer-name,  # needed for test fixtures
         simplifiable-if-expression,
         subprocess-popen-preexec-fn,
-        super-with-arguments,
         unexpected-keyword-arg,
         unnecessary-dunder-call,
         unnecessary-pass,
@@ -415,7 +414,6 @@ disable=raw-checker-failed,
         unused-variable,
         use-dict-literal,
         use-list-literal,
-        useless-object-inheritance,
         # Cannot remove yet due to inadequacy of rules
         inconsistent-return-statements,  # doesn't notice that fail_json() does not return