Comment 3 for bug 1820840

> The stable/ubuntu-19.04 track has been created for core18, should fix this.

As discussed on IRC, I don't think this is the right fix. We do NOT want a proliferation of core18 snaps on different per-Ubuntu-release branches with subtle differences; we expect the base snap to be a common base that works on all target classic releases and in support of all snaps using that base.

So the bug here is in livecd-rootfs not knowing to treat core18 specially. The images are building again, but they're building WRONG, seeding core18 from the stable/ubuntu-19.04 channel instead of the stable channel they should be using.

I also don't think the core18 snap belongs in the seed (where it has now been added). We do have to seed the gnome-3-28-1804 snap currently, and that does (and should) carry a per-Ubuntu-release branch, but I think base snaps should not have to be seeded directly for the same reason we don't manually seed all the dependencies of the leaf packages.

So I would like to see:

 - livecd-rootfs updated to know when it needs core18 as a base for one of the seeded snaps
 - livecd-rootfs to detect when *all* seeded snaps specify a base:, and if so, seed snapd instead of core
 - core18 removed from the seed.