Remove registry from exit_json because misleading docker-py is not returning the name of the registry if already logged in. It can differ from the registry specified by the user, which was return as registry.

lib/ansible/modules/extras/cloud/docker/docker_login.py

@@ -229,7 +229,7 @@ def main():
     try:
         manager = DockerLoginManager(module)
         manager.login()
-        module.exit_json(changed=manager.has_changed(), msg=manager.get_msg(), registry=manager.registry)
+        module.exit_json(changed=manager.has_changed(), msg=manager.get_msg())
 
     except Exception as e:
         module.fail_json(msg="Module execution has failed due to an unexpected error", error=repr(e))