docs: def _perform_power_op(self, oper):
          """Perform requested power operation.
  
          :param oper: Type of power button press to simulate.
                       Supported values: 'ON', 'ForceOff', 'ForceRestart' and
                       'Nmi'
          :raises: IloError, on an error from iLO.
          """
  
          power_settings = {"Action": "Reset",
                            "ResetType": oper}
          systems_uri = "/rest/v1/Systems/1"
  
          status, headers, response = self._rest_post(systems_uri, None,
                                                      power_settings)
          if status >= 300:
              msg = self._get_extended_error(response)
              raise exception.IloError(msg)