Bug 2102907

As part of https://fedoraproject.org/wiki/Changes/BIOSBootISOWithGrub2 , we had to change the pungi configuration for Fedora Rawhide composes to use `createiso_use_xorrisofs = True` - that was required for having x86_64 ISOs built by pungi just re-use the bootloader bits from the base boot.iso (built by lorax) that they work from.

I just noticed (sorry I didn't spot this earlier) that, since making that change, the ppc64le Server DVD ISOs do not boot. All other ppc64le ISOs do boot. I believe all the other ISOs are built directly by lorax; the Server DVD ISO is the only one that's built by pungi based from an initial image produced by lorax.

Unfortunately, since I didn't notice it in time, the logs from the most recent compose that still worked "the old way" have been garbage collected (unless nirik can reconstruct them from anywhere). But this is the most recent failed task: https://koji.fedoraproject.org/koji/taskinfo?taskID=88911314 . https://kojipkgs.fedoraproject.org//work/tasks/1314/88911314/root.log has all the xorriso logs.

The boot failure looks like the attached screenshot, on a qemu VM: the firmware complains "failed to load CHRP boot loader.failed to load CHRP boot loader."

This is an automatic FE for F37 Beta per https://fedoraproject.org/wiki/QA:SOP_freeze_exception_bug_process#Automatic_freeze_exceptions "Complete failure of any non-release-blocking image to boot at all under any circumstance - "DOA" image", marking as such.