Code review comment for lp:~paelzer/curtin/bug-1574113-derived-repositories

Since we co-work on a branch that we can jointly push to now there is a new MP at https://code.launchpad.net/~ubuntu-server/curtin/bug-1574113-derived-repositories/+merge/301362

This old MP here is kept open to have the discussion history available (not sure if it would go away when rejecting the old MP).