We have something like pvpanic device. However, in some cases it does
not have any address assigned, in which case we produce this ugly XML
(still valid though):
<devices>
<emulator>/usr/bin/qemu</emulator>
...
<panic>
</panic>
</devices>
Lets format "<panic/>" instead.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
