Since the PXE tester runs rather slow on ppc64 with tcg, there
is a chance that we hit the 60 seconds timeout on machines that
have a heavy CPU load. So let's increase the timeout to ease
the situation.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>