As we saw with F23 testing, qemu32 isn't really supported CPU. Also,
we cannot be sure that std is really supported graphics. This changes MACHINE
variables to use host CPU with 64bit machines (moreover, this is the case in
BOS now). It uses kvm32 CPU for pure-32bit CPUs - I don't know whether it's
better than qemu32 (nobody was able to tell me), but at least it works OK.
I've also changed graphics to qxl. Even though we aren't using SPICE, qxl has
better support (and higher priority) and it seems to work OK with VNC. Fixes T637.