Pktgen does not support for windows guest, disable it.

Signed-off-by: Cong Li <coli@redhat.com>
Merge pull request #220 from CongSmile/pktgen

Pktgen does not support for windows guest, disable it.
qemu.tests: Add a new case for test multi queue for virtio scsi

Signed-off-by: Yiqiao Pu <ypu@redhat.com>