When redoing the website we deleted the libvirtLogo.png file
not remembering that the test driver screenshot API impl
relied on it.

Rather than having the test driver use the logo as a side
effect, give it its own dedicated image to use. This is
installed in /usr/share/libvirt/test-screenshot.png and
is taken from a NeXT Cube running WorldWideWeb[1]. The
very first web browser in existance, running on the
hardware it was originally written on.

[1] https://en.wikipedia.org/wiki/WorldWideWebSigned-off-by: NDaniel P. Berrange <berrange@redhat.com>