code: def list_users(self):
          
          lines = output_lines(self.exec_rabbitmqctl_list('users'))
          return [_parse_rabbitmq_user(line) for line in lines]
docs: Run the ``list_users`` command and return a list of tuples describing
          the users.
  
          :return:
              A list of 2-element tuples. The first element is the username, the
              second a list of tags for the user.