Cleanups and fixes to cli

* Mark methods which are really functions as staticmethod
* Fix calls to other staticmethods to use the subclass rather than the
  base class so that any inheritance overriding will be honored.
* Remove unnecessary logic and dead code
* Fix a typo in a docstring of how to implement subclass init_parser()
  methods
* Call superclass's post_process_args in ansible-doc
* Fix copyright comment according to suggested practice

lib/ansible/cli/playbook.py

@@ -179,7 +179,8 @@ class PlaybookCLI(CLI):
         else:
             return results
 
-    def _flush_cache(self, inventory, variable_manager):
+    @staticmethod
+    def _flush_cache(inventory, variable_manager):
         for host in inventory.list_hosts():
             hostname = host.get_name()
             variable_manager.clear_facts(hostname)