respect undefined config setting

lib/ansible/executor/playbook_executor.py

@@ -81,7 +81,7 @@ class PlaybookExecutor:
                     # Create a temporary copy of the play here, so we can run post_validate
                     # on it without the templating changes affecting the original object.
                     all_vars = self._variable_manager.get_vars(loader=self._loader, play=play)
-                    templar = Templar(loader=self._loader, variables=all_vars, fail_on_undefined=False)
+                    templar = Templar(loader=self._loader, variables=all_vars)
                     new_play = play.copy()
                     new_play.post_validate(templar)
 

lib/ansible/executor/task_queue_manager.py

@@ -224,7 +224,7 @@ class TaskQueueManager:
                     play.vars[vname] = self._do_var_prompt(vname, private, prompt, encrypt, confirm, salt_size, salt, default)
 
         all_vars = self._variable_manager.get_vars(loader=self._loader, play=play)
-        templar = Templar(loader=self._loader, variables=all_vars, fail_on_undefined=False)
+        templar = Templar(loader=self._loader, variables=all_vars)
 
         new_play = play.copy()
         new_play.post_validate(templar)