Comment 8 for bug 1635181

I just spent 4+ hours trying to figure out why every bit of documentation (info, ask.ubunutu, etc) about booting multiple partitions wasn't working on a stock ubuntu-18.04.1-live-server-amd64.iso install. Only ended up finding it by putting a `set -x` in `/etc/grub.d/30_os-prober`, seeing it fail with `GRUB_DISABLE_OS_PROBER=true`, and doing a `find|grep` on all of `/etc` to find the culprit.

While you could fix the `maybe-ubiquity` bit by making it append, I'm not sure how you fix the os-prober part other than just not doing it in the first place? I'm guessing it simplifies things at install time, but is there a reason to silently (or at all) disable that feature once the initial install is done?