Fix fullstack for cirros image not found
Fix fullstack for cirros image not found

Devstack use 0.3.5 as default cirros version now, and the default image
format is qcow2 now.

https://review.openstack.org/#/c/432793/
https://review.openstack.org/#/c/338435/

Change-Id: I386201ae651746a1220ba2465b0715cb7345696c

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow