grub_dpkg removes configs with backup EFI partitions in grub-efi/install_devices debconf key

[medicalwei]

Bug report

When the system is set up with multiple EFI System Partitions (ESPs), for example, RAID setup, curtin sets up multiple partitions in grub-efi/install_devices.

However, grub_dpkg module changes grub-efi/install_devices to single device mounted in /boot/efi, which can then cause backup ESP partition(s) not to be upgraded when GRUB package is upgraded.

The type of the debconf field grub-efi/install_devices is also changed from multiselect to string.

Note that, the backup EFI partitions feature is Ubuntu specific, and does not exist in Debian. I am not sure whether we should note it but not to handle this issue, as simply disabling this module can avoid this problem.

Steps to reproduce the problem

• Have a multiple disk system, install Ubuntu Server 24.04 LTS with multiple boot drives
• After installation, run debconf-show grub-efi-amd64 (or equivalent), ensure in grub-efi/install_devices two partitions in /dev/disks/by-id are listed
• Provision the system with cloud-init once, run debconf-show grub-efi-amd64 again

Expected:

• The latter should return 2 partitions

Actual:

• The latter returns single partition currently mounted in /boot/efi

Environment details

• Cloud-init version: 26.1-0ubuntu1~24.04.1
• Operating System Distribution: Ubuntu 24.04 LTS
• Cloud provider, platform or installer type: NoCloud

cloud-init logs

cc_grub_dpkg.py[DEBUG]: considering these device symlinks: /dev/disk/by-label/boot,...,
  /dev/disk/by-id/nvme-Micron_7450_MTFDKBA480TFR_254954CD71E8-part1,
  /dev/disk/by-id/nvme-Micron_7450_MTFDKBA480TFR_254954CD71E8_1-part1,
  /dev/disk/by-id/nvme-eui.000000000000000100a0752554cd71e8-part1
cc_grub_dpkg.py[DEBUG]: filtered to these disk/by-id symlinks: <the three above>
cc_grub_dpkg.py[DEBUG]: selected /dev/disk/by-id/nvme-Micron_7450_MTFDKBA480TFR_254954CD71E8-part1
cc_grub_dpkg.py[DEBUG]: Setting grub debconf-set-selections with
  'grub-pc grub-efi/install_devices string /dev/disk/by-id/nvme-Micron_...CD71E8-part1