Add four tests of the XML -> argv handling for the PPC64 pseries machine.

The first is just a basic test of a bare bones machine.

The three others test various aspects of the spapr-vio address handling.

It seems that currently we can't include network devices, doing so leads
to a segfault because the network driverState is not initialised. Working
around that leads us to the problem that the 'default' network doesn't
exist. So for now just leave network devices out.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>