The redfish management interface is not boot_mode aware

[Ilya Etingof]

Redfish spec allows for configuring boot mode (e.g. UEFI/BIOS) to the the BM node.

With current redfish driver, it is not possible to change boot mode - one can only rely on system default (which is typically legacy BIOS).

We should probably pull the desired boot mode from `instance_info` or `properties/capabilities` and convey it to appropriate [1] Redfish call.

1. https://github.com/openstack/ironic/blob/7c5115747a37ea49c8aa47ff6159096d5fa75b2e/ironic/drivers/modules/redfish/management.py#L106

[Dmitry Tantsur (divius)]

This should be split into two fixes, I think.

The first just reads the boot mode and makes sure ironic does the right PXE stuff (sending ipxe.efi instead of undionly.kpxe, etc). This is clearly backportable, and has to be backported to Pike.

The second will allow setting boot mode via boot_mode capability. This may not be backportable, even though we treat it as a bug. We'll have to look at the actual fix to decide.

Thanks!

P.S.
Reading boot mode with sushy: https://github.com/openstack/sushy/blob/8fe2904a62b0f56dc3fc3fefc5a5a746911ce891/sushy/resources/system/system.py#L43-L44 (it will be accessible as system.boot.mode)
Setting: https://github.com/openstack/sushy/blob/8fe2904a62b0f56dc3fc3fefc5a5a746911ce891/sushy/resources/system/system.py#L204-L205