[xen-tools] --ip=auto

Hey,

Just a quick note that I tested out the IP auto-allocation mechanism
today and it works pretty well (although still awaiting the addition
of the inverse operation to xen-delete-image :) no big rush though).
However, I found a bug, namely that the script doesn't re-add newlines
to the ips.txt file after it chomps them, so after the first use you
end up with a single-line file.

I didn't actually test it to see if that breaks subsequent uses, but I
assumed it would, and added a few characters to append the newline
when adding the line to the array, and it seems to work just fine with
that change in place.

Thought you might want a heads-up :)

Thanks,
Jeff