[iRMC] Fix overlooked case in merged patch which deals with iRMC firmware IPMI incompatibility

In the past patch[1] which handles iRMC firmware's IPMI incompatibility[2], we chose to add flag `irmc_ipmi_succeed` in `driver_internal_info` to indicate whether iRMC firmware supports IPMI connection.
If that flag indicates iRMC firmware doesn't support IPMI connection, iRMC driver uses Redfish API of iRMC firmware to do Ironic operation. On the other hand, if that flag indicates iRMC firmware supports IPMI connection, iRMC driver uses IPMI against iRMC firmware to do Ironic operation.
That flag is set and periodically updated by `irmc` `power_interface`.

However iRMC driver supports `ipmitool` and `irmc` as `power_interface`. When `power_interface` is set to `ipmitool`, above flag `irmc_ipmi_succeed` will not be updated and rest of iRMC driver code fails to handle iRMC firmware's IPMI incompatibility properly.

To handle this overlooked situation, I add following logic in the iRMC driver's code where iRMC driver checks `irmc_ipmi_succeed` flag:
* Check if `power_interface` is set to `ipmitool`, if so, use IPMI to do Ironic operation. This is enough to handle situation because `verifying` step checks if IPMI connection to iRMC succeeds.

[1] https://review.opendev.org/c/openstack/ironic/+/865075
[2] https://storyboard.openstack.org/#!/story/2010396