Code review comment for lp:~axwalk/goose/nova-availability-zones

Do any of our openstack clouds actually support this extension? Neither
canonistack nor HP seem to. I'm not totally up to dat on current plans,
but this seemed to be a dead end a year ago, with different mechanisms
talked about as fulfilling the role that weren't availabilty zone based.

https://codereview.appspot.com/103900045/