virttest: Add virtio-serial-pci for virtio console device

We do not support multiple virtconsole for one virtio-serial-pci.
So add it when the virtio_port_type is console.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #1500 from ypu/virtio_console

virttest: Add virtio-serial-pci for virtio console device