When no video device is specified in config we should set both
hvm.nographic to 1 and hvm.vga.kind to NONE.

Without hvm.vga.kind=LIBXL_VGA_INTERFACE_TYPE_NONE both -nographic and
-device 'cirrus-vga' are on qemu cmdline.
Signed-off-by: NArtur Puzio <contact@puzio.waw.pl>
Reviewed-by: NJim Fehlig <jfehlig@suse.com>