qemuxml2argvtest: Don't overwrite driver stateDir

qemuxml2argvtest: Don't overwrite driver stateDir

This is a very historic artefact. Back in the old days of
830ba76c3e when we had macros to add arguments onto qemu command
line (!) we thought it was a good idea to let qemu write out the
PID file. So we passed -pidfile $stateDir/$domName onto the
command line. Thus, in order for tests to work we needed stable
stateDir in the qemu driver. Unfortunately, after 16efa11aa696
where stateDir is mkdtemp()-d, this approach lead to a leak of
temp dir.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>