Two fixes to action plugins

* Fix the task_vars parameter to not default to a mutable type (dict)
* Implement invocation in the base class's run() method have each action
  module call the run() method's implemention in the base class.
* Return values from the action plugins' run() method takes the return
  value from the base class run() method into account so that invocation
  makes its way to the output.

Fixes #12869

test/integration/roles/test_good_parsing/tasks/main.yml

@@ -155,11 +155,9 @@
     that:
       - complex_param == "this is a param in a complex arg with double quotes"
 
-#- name: test variable module name
-#  action: "{{ variable_module_name }} msg='this should be debugged'"
-#  register: result
-#
-#- debug: var=result
+- name: test variable module name
+  action: "{{ variable_module_name }} msg='this should be debugged'"
+  register: result
 
 - name: assert the task with variable module name ran
   assert: