[Merge] ~mvo/livecd-rootfs:snap-validate-seed into livecd-rootfs:ubuntu/master

[Robert C Jennings]

Review: Approve

mvo, I did a test build last night for the ubuntu-cpc project (with $CHROOT_ROOT) and it was successful.
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https://code.launchpad.net/~mvo/livecd-rootfs/+git/livecd-rootfs/+merge/370065
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