I mounted the iso on /mnt and extracted the kernel and ramdisk from /mnt/boot . Then I went to virt-manager and selected 'additional configuration before boot', selected direct kernel boot, and entered the file names for the kernel and ramdisk.
That done, the VM booted and progressed with the install. So it looks that the problem is that the ISOs are set up in a way which does not allow the virtual boot firmware to find the kernel and ramdisk. Is this fixable ?
