It turns out we do need to create the machine-id for the same reason
as on 8. This was being hidden by the bootloader choosing the root
disk label from the host (see the dependent change).
Change I3b518802d681b888916a5cc6a3dcf7e1b537da1e has modified the
testing to use a different root-disk label, which should help catch
this in the fututure.
Depends-On: https://review.opendev.org/c/zuul/nodepool/+/853574
Change-Id: I64de66cac25fd2e051780fb4812e075c647eb76e