[Merge] ~philroche/livecd-rootfs/+git/livecd-rootfs:bugfix/ubuntu-cpc-lp-2054103-grub-pc-debconf into livecd-rootfs:ubuntu/master

[Philip Roche]

This can be merged before the grub changes addressing https://code.launchpad.net/bugs/2054103 land.
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https://code.launchpad.net/~philroche/livecd-rootfs/+git/livecd-rootfs/+merge/461062
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