fix ownership of containerd/docker sysext files

[jepio]

fix ownership of containerd/docker sysext files

Systemd units shipped with the sysext were accidentally owned by the sdk user because we were telling cp to preserve ownership, and the files come from the cloned repo which is owned by the sdk user. Fix the cp invocation and add a check for wrong files before the sysext is created.

See: flatcar/Flatcar#1525

How to use

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Testing done

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• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/10664680809

[jepio]

Cherry-picked to stable/beta/alpha, lts doesn't have sysext docker/containerd yet.
Checked the image produced in GHA:

NAME="Flatcar Container Linux by Kinvolk"
ID=flatcar
ID_LIKE=coreos
VERSION=4077.0.0+nightly-20240829-2100-3-g412298cd39
VERSION_ID=4077.0.0
BUILD_ID=nightly-20240829-2100-3-g412298cd39
SYSEXT_LEVEL=1.0
PRETTY_NAME="Flatcar Container Linux by Kinvolk 4077.0.0+nightly-20240829-2100-3-g412298cd39 (Oklo)"
ANSI_COLOR="38;5;75"
HOME_URL="https://flatcar.org/"
BUG_REPORT_URL="https://issues.flatcar.org"
FLATCAR_BOARD="amd64-usr"
CPE_NAME="cpe:2.3:o:flatcar-linux:flatcar_linux:4077.0.0+nightly-20240829-2100-3-g412298cd39:*:*:*:*:*:*:*"
core@localhost /etc/extensions $ sudo mount containerd-flatcar.raw /mnt/
core@localhost /etc/extensions $ ls -laR /mnt/usr/lib/systemd/system/
/mnt/usr/lib/systemd/system/:
total 2
drwxr-xr-x. 4 root root  99 Aug 30 09:36 .
drwxr-xr-x. 3 root root  29 Aug 30 07:57 ..
-rw-r--r--. 1 root root 667 Aug 30 07:57 containerd.service
drwxr-xr-x. 2 root root  49 Aug 30 09:36 multi-user.target.d
drwxr-xr-x. 2 root root  41 Aug 30 07:57 multi-user.target.wants

/mnt/usr/lib/systemd/system/multi-user.target.d:
total 1
drwxr-xr-x. 2 root root 49 Aug 30 09:36 .
drwxr-xr-x. 4 root root 99 Aug 30 09:36 ..
-rw-r--r--. 1 root root 34 Aug 30 09:36 10-containerd-service.conf

/mnt/usr/lib/systemd/system/multi-user.target.wants:
total 1
drwxr-xr-x. 2 root root 41 Aug 30 07:57 .
drwxr-xr-x. 4 root root 99 Aug 30 09:36 ..
lrwxrwxrwx. 1 root root 21 Aug 30 07:57 containerd.service -> ../containerd.service
core@localhost /etc/extensions $ sudo umount /mnt/
core@localhost /etc/extensions $ sudo mount docker-flatcar.raw /mnt/
core@localhost /etc/extensions $ ls -laR /mnt/usr/lib/systemd/system/
/mnt/usr/lib/systemd/system/:
total 3
drwxr-xr-x. 3 root root   82 Aug 30 09:36 .
drwxr-xr-x. 4 root root   44 Aug 30 07:57 ..
-rw-r--r--. 1 root root 1474 Aug 30 07:57 docker.service
-rw-r--r--. 1 root root  198 Aug 30 07:57 docker.socket
drwxr-xr-x. 2 root root   44 Aug 30 09:36 sockets.target.d

/mnt/usr/lib/systemd/system/sockets.target.d:
total 1
drwxr-xr-x. 2 root root 44 Aug 30 09:36 .
drwxr-xr-x. 3 root root 82 Aug 30 09:36 ..
-rw-r--r--. 1 root root 29 Aug 30 09:36 10-docker-socket.conf