[train] paunch: exit module if config doesn't exist

It's possible that the step directory doesn't exist in a deployment,
just quit the module with no change and move on.

It'll avoid running paunch with empty config.
This will be backported to Train.

Change-Id: I3a5fc2214e7068f1e7aacc0e7a8a681c3f9715e9
(cherry picked from commit b2fe3f2d61)

tripleo_ansible/ansible_plugins/modules/paunch.py

@@ -166,6 +166,9 @@ class PaunchManager:
                                                    log_file=self.log_file)
 
         if self.config:
+            # Do nothing if config path doesn't exist
+            if not os.path.exists(self.config):
+                self.module.exit_json(**self.results)
             if self.config.endswith('.json'):
                 self.module.warn('Only one config was given, cleanup disabled')
                 self.cleanup = False