[Merge] ~xnox/livecd-rootfs:fix-desktop-live-kernel-renames into livecd-rootfs:ubuntu/master

[Dimitri John Ledkov]

separately, we can patch ubuntu-cdimage / livecd-roots / ubuntu-image to just generate the one and only kernel/initrd for a single kernel build; and always use it as default. And then any extra ones generate under unique names and be able to enable booting them too as needed.

Such that we could in theory build / change flavours dynamically, without need to patch all the tools 4 times to add desktop on "generic-64k" for arm64 for example.
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https://code.launchpad.net/~xnox/livecd-rootfs/+git/livecd-rootfs/+merge/452363
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