docs: def _update_persistent_boot(self, device_type=[], persistent=False):
          """Changes the persistent boot device order in BIOS boot mode for host
  
          Note: It uses first boot device from the device_type and ignores rest.
  
          :param device_type: ordered list of boot devices
          :param persistent: Boolean flag to indicate if the device to be set as
                             a persistent boot device
          :raises: IloError, on an error from iLO.
          :raises: IloCommandNotSupportedError, if the command is not supported
                   on the server.
          """
          tenure = 'Once'
          new_device = device_type[0]
          # If it is a standard device, we need to convert in RIS convention
          if device_type[0].upper() in DEVICE_COMMON_TO_RIS:
              new_device = DEVICE_COMMON_TO_RIS[device_type[0].upper()]
  
          if persistent:
              tenure = 'Continuous'
  
          systems_uri = "/rest/v1/Systems/1"
          # Need to set this option first if device is 'UefiTarget'
          if new_device is 'UefiTarget':
              system = self._get_host_details()
              uefi_devices = (
                  system['Boot']['UefiTargetBootSourceOverrideSupported'])
              iscsi_device = None
              for device in uefi_devices:
                  if device is not None and 'iSCSI' in device:
                      iscsi_device = device
                      break
  
              if iscsi_device is None:
                  msg = 'No UEFI iSCSI bootable device found'
                  raise exception.IloError(msg)
  
              new_boot_settings = {}
              new_boot_settings['Boot'] = {'UefiTargetBootSourceOverride':
                                           iscsi_device}
  
              status, headers, response = self._rest_patch(systems_uri, None,
                                                           new_boot_settings)
              if status >= 300:
                  msg = self._get_extended_error(response)
                  raise exception.IloError(msg)
  
          new_boot_settings = {}
          new_boot_settings['Boot'] = {'BootSourceOverrideEnabled': tenure,
                                       'BootSourceOverrideTarget': new_device}
          status, headers, response = self._rest_patch(systems_uri, None,
                                                       new_boot_settings)
          if status >= 300:
              msg = self._get_extended_error(response)
              raise exception.IloError(msg)