tests: add more tests for graphics devices

this patch adds a few more sanity tests for
the graphic devices.

Change-Id: I6724ee2c5ce393272b40aa7b08bc5f864123fdc5
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27901
Reviewed-by: Dan Kenigsberg <danken@redhat.com>