qemu: Set capabilities properly for tests

qemu: Set capabilities properly for tests

Several tests were not specifying the necessary qemu capabilities for
what they were testing. Due to the way that the video devices are
currently validated, this is not causing any problems. But a change to
video device validation in a following patch would have exposed this
issue and resulted in multiple test failures about the domain
configuration not supporting particular video models.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>