🐛 Empty machine-id instead of removing it

[Itxaka]

We used to rely on a hidden feature of sysinfo that created a filled machine-id during initramfs so systemd did not trigger the first boot service.

Now on the newer agent versions, that hidden functionality has gone away so if we remove it teh file, systemd will think that this is a new system and will do some work behind our back initializing and break things around.

So we need to create en empty machine-id file so systemd knows that we dont want to run the first boot services/target

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2773

[jimmykarily]

I'd wish systemd had a way to disable the firstboot service without hacking with machine-id. But it is what it is I guess.

[Itxaka]

I'd wish systemd had a way to disable the firstboot service without hacking with machine-id. But it is what it is I guess.

https://man.archlinux.org/man/machine-id.5.en#FIRST_BOOT_SEMANTICS

1.The kernel command argument systemd.condition_first_boot= may be used to override the autodetection logic, see [kernel-command-line(7)](https://man.archlinux.org/man/kernel-command-line.7.en).
2.Otherwise, if /etc/machine-id does not exist, this is a first boot. During early boot, systemd will write "uninitialized\n" to this file and overmount a temporary file which contains the actual machine ID. Later (after first-boot-complete.target has been reached), the real machine ID will be written to disk.
3.If /etc/machine-id contains the string "uninitialized", a boot is also considered the first boot. The same mechanism as above applies.
4.If /etc/machine-id exists and is empty, a boot is not considered the first boot. systemd will still bind-mount a file containing the actual machine-id over it and later try to commit it to disk (if /etc/ is writable).
5.If /etc/machine-id already contains a valid machine-id, this is not a first boot.

We could add the kernel cmdline as well to avoid this, but we will still have issues with the machine-id I think as we need to work around immutability and such