`bootc install to-filesystem` fails to find PReP partition

I think there's some back-and-forth and shared code between `bootupd` and `bootc` here. It seems the fix was added in `bootc` 1.15.2 but `bootupd` requires `bootc-internal-blockdev = "1.15.1"`; perhaps we need an updated `bootupd`? A dependabot PR for that is open: https://github.com/coreos/bootupd/pull/1102

---

I have the following setup of devices and partitions mounted to `/run/osbuild/mounts`. When calling `bootc install to-filesystem ... /run/osbuild/mounts` it errors out unable to find the PReP partition. I think the following PRs and issues are related:

1. https://github.com/bootc-dev/bootc/pull/2000 initial change to partition scanning?
2. https://github.com/osbuild/osbuild/pull/2428 discussion about exposing udev in `osbuild` which was determined to not be a good idea.
3. https://github.com/bootc-dev/bootc/pull/2169 fallback implementation using blkid in `bootc`.

Here is some additional information of what I see; all of these commands are executed inside the `bubblewrap` sandbox that `osbuild` runs `bootc` in. We are running `bootc` 1.15.2.

This was reported to us by the COPR folks through: https://github.com/osbuild/bootc-image-builder/issues/1223 and I've asked the CoreOS folks to confirm and they see the same issue.

`bootc` has definitely found the appropriate loopback device and the loopback device seems to contain all the necessary information.

```
bash-5.3# fdisk -l /dev/loop0
Disk /dev/loop0: 10 GiB, 10737418240 bytes, 20971520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 5E498532-F66F-45F7-856C-3947540949ED

Device Start End Sectors Size Type
/dev/loop0p1 2048 10239 8192 4M PowerPC PReP boot
/dev/loop0p2 10240 2107391 2097152 1G Linux filesystem
/dev/loop0p3 2107392 20971486 18864095 9G Linux filesystem
```

The exact call I think `bootc` 1.15.2 is using to find things returns the correct GUID.

```
bash-5.3# blkid -p -o export /dev/loop0p1
DEVNAME=/dev/loop0p1
PART_ENTRY_SCHEME=gpt
PART_ENTRY_UUID=e13d84b4-c453-4c9f-9bcd-9661b864a68b
PART_ENTRY_TYPE=9e1a2d38-c612-4316-aa26-8b49521e5a8b
PART_ENTRY_NUMBER=1
PART_ENTRY_OFFSET=2048
PART_ENTRY_SIZE=8192
PART_ENTRY_DISK=7:0
```

When calling `bootc install to-filesystem ...` I get the following error:

```
bootc install to-filesystem --source-imgref containers-storage:[overlay@/run/osbuild/containers/storage2+/run/containers/storage:additionalimagestore=/run/osbuild/containers/storage]23d96bab9abd0129245c0dd2208361191a0535f0915842152f98fc922898c761 --skip-fetch-check --generic-image --karg rw --karg console=tty0 --karg console=ttyS0 --target-imgref quay.io/fedora/fedora-bootc:latest /run/osbuild/mounts
Installing image: docker://quay.io/fedora/fedora-bootc:latest
Initializing ostree layout
layers already present: 0; layers needed: 65 (927.5 MB)
Deploying container image...done (38 seconds)
Bootloader: grub
Installing bootloader via bootupd
error: boot data installation failed: installing component BIOS to device /dev/loop0: installing GRUB on /dev/loop0: Failed to find PReP partition with GUID 9E1A2D38-C612-4316-AA26-8B49521E5A8B
error: Installing to filesystem: Installing bootloader: Failed to run command: Command {
program: "bwrap",
args: [
"bwrap",
"--bind",
"/run/osbuild/mounts/ostree/deploy/default/deploy/51899f2ccb49f3b456dce76b8e467f446f87586945686a915026aac8a707addf.0",
"/",
"--proc",
"/proc",
"--dev-bind",
"/dev",
"/dev",
"--bind",
"/sys",
"/sys",
"--tmpfs",
"/run",
"--bind",
"/run",
"/run",
"--bind",
"/run/osbuild/mounts/boot",
"/boot",
"--bind",
"/run/osbuild/mounts",
"/sysroot",
"--setenv",
"PATH",
"/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin",
"--",
"bootupctl",
"backend",
"install",
"--write-uuid",
"--filesystem",
"/",
"/",
],
create_pidfd: false,
}
```

Additional (potentially not very useful) bits:

```
bash-5.3# blkid -o full
/dev/loop0p3: LABEL="root" UUID="aa3cff58-c8e4-4794-84b2-89d127f4a523" BLOCK_SIZE="512" TYPE="xfs" PARTUUID="27ad1867-5325-4e23-90fa-dc960c625664"
/dev/loop0p2: LABEL="boot" UUID="a2d17c6c-de8c-49e1-abc0-96614494e955" BLOCK_SIZE="512" TYPE="xfs" PARTUUID="3c8b17a4-3ca4-47e3-aa72-ee510159a851"
/dev/loop0p1: PARTUUID="e13d84b4-c453-4c9f-9bcd-9661b864a68b"
```

```
bash-5.3# findmnt -R /run/osbuild/mounts
TARGET SOURCE FSTYPE OPTIONS
/run/osbuild/mounts /dev/loop0p3 xfs rw,nosuid,nodev,relatime,seclabel,inode64,logbufs=8,logbsize=32k,noquota
`-/run/osbuild/mounts/boot /dev/loop0p2 xfs rw,nosuid,nodev,relatime,seclabel,inode64,logbufs=8,logbsize=32k,noquota
```

```
bash-5.3# bootc --version
bootc 1.15.2
```