fix: Set the required debconf settings to allow for non interactive grub updates in cloud images (LP: #2054103)
As part of addressing LP: #2054103 [1] an update to grub-pc added a feature to be able to ensure that grub-pc
installation can happen noninteractively on cloud images.
This change is equivalent to running
```
debconf-set-selections grub-pc grub-efi/cloud_style_installation boolean true
debconf-set-selections grub-pc grub-pc/cloud_style_installation boolean true
```
These were introduced optionally to determine the install device using
`grub-probe` dynamically instead of having to fill the `grub-pc/install-devices`
debconf entry.
[1] https://bugs.launchpad.net/cloud-images/+bug/2054103
MP: https://code.launchpad.net/~philroche/livecd-rootfs/+git/livecd-rootfs/+merge/461062
As part of addressing LP: #2054103 [1] an update to grub-pc added a feature to be able to ensure that grub-pc
installation can happen noninteractively on cloud images.
This change is equivalent to running
```
debconf-set-selections grub-pc grub-efi/cloud_style_installation boolean true
debconf-set-selections grub-pc grub-pc/cloud_style_installation boolean true
```
These were introduced optionally to determine the install device using
`grub-probe` dynamically instead of having to fill the `grub-pc/install-devices`
debconf entry.
[1] https://bugs.launchpad.net/cloud-images/+bug/2054103
There was a time historically where Launchpad buildd might have relied
on that behaviour, but this shouldn't be the case anymore as it sets
priority manually when building backports.
Meanwhile any other builds using buildd images (e.g. snapcraft)
shouldn't default to backports unless required. (lp: #2009871)
Refs:
- [1] https://git.launchpad.net/launchpad-buildd/commit?id=c2ebcb6752
Per the comments, BASE_SEED was initially used to identify the seed in the
flavor to use for identifying preseeded snaps, and later was also used to
identify which "minimal-remove" seed to apply to an image.
The first usage is now obsolete after a refactor; we now correctly detect
snaps from any of the included seeds without needing an explicit
declaration.
The second usage only applies to installer images that are NOT using layered
squashfs, since for these images 'minimal' is a separate squashfs layer
rather than a list of packages to remove after the fact.
Refactor this code to eliminate pointless definitions of BASE_SEED and
define it only for the subset of flavors today that:
- have a 'minimal-remove' seed
- are not using layered squashfs.
The cloud-images logic is now special case for ubuntu-wsl to not require
ending with project_prefix. Readd it first, which will allow us to
ensure backward compability on cloud-images.ubuntu.com
