Remove setting of DEFAULT_IMAGE_NAME to non exit image

Due to devstack logic of setting the two different images in
tempest, we has to set the DEFAULT_IMAGE_NAME to non exit image
which broke ironic. Below patch fix the logic in devstack so
we do not need to set non exit image in DEFAULT_IMAGE_NAME
- https://review.opendev.org/c/openstack/devstack/+/886795/

Change-Id: I22f343c9d8ca8ec4044e2d6877378d29383e2890
1 file changed