[Merge] ~tobijk/livecd-rootfs/+git/livecd-rootfs:feature/implicit-core-seeding into livecd-rootfs:ubuntu/master

[Tobias Koch]

This has been tested as much as possible. The manifests look correct and on cpc images snaps are properly pre-seeded.
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https://code.launchpad.net/~tobijk/livecd-rootfs/+git/livecd-rootfs/+merge/365878
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~tobijk/livecd-rootfs/+git/livecd-rootfs:feature/implicit-core-seeding into livecd-rootfs:ubuntu/master.