tests: add test to check VirtQueue object

An uninitialised VirtQueue object or one with Vring.align field
set to zero(0) could lead to arithmetic exceptions. Add a unit
test to validate it.

Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
