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.

A glossary doesn't belong in the tutorial, which expects the user to
know nothing of the service. That belonds in the Howto section, where
we expect to learn a little more about the service before doing things.

I added that TODO based on a misunderstanding of the function of the
private network between the Ganeti nodes. It's not there to provide a
private network between *instances*, but really just the nodes, for
DRBD and Ganeti traffic.

So it makes no sense to allocate private IPs to the instances in that context.

We remove the `gnt-node list` command because it's included in the other.

The rationale is that this part is more rarely used and definitely
more complex than a Howto.

The rationale is that it is yet one more argument and the balancer might cancel that later anyways.