While this procedure is available in a billion places already, this is
the kind of stuff that you mess up when you get awaken at 3AM and can
barely type.

Let's see if we can get the human error out of the equation a little
more by helping those poor infected water bags a little.

this is starting to look like a thing ansible should be doing

we could have also used the new swap UUID and edited the fstab, but
that would have required more steps:

 1. mount the filesystem
 2. edit fstab
 3. unmount

... and another thing to redo after the last resync.

By enforcing a UUID from the start, we don't need to edit the fstab at
all. I can't think of a compelling reson why reusing the UUID might be
a problem.

The thing just works. It does everything we need except maybe picking
arbitrary labels for RAID arrays (and that might even be possible to
work around).

By using a configuration file and setup-storage, we bring ourselves
closer to standardizing and automating the installer.

setup-storage also has the advantage of being idempotent, mostly: I
was able to run and rerun it multiple times from the rescue shell. The
only thing I had to do was to close LUKS devices, if I remember
correctly. But it was much easier to test than a shell script.

Finally, it provides nice features like dumping the fstab, crypttab
and mdadm.conf for us to use. We don't use those just yet.

It also provides a shell script that can be sourced to get various
targets, which we use.