tests/vm: move vga setup

Move '-device VGA' from basevm.py to the guests, so they have
the chance to opt out and run without display device.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200310083218.26355-3-kraxel@redhat.com>
Message-Id: <20200323161514.23952-3-alex.bennee@linaro.org>
6 files changed