Comment 2 for bug 1376334

It feels like this could be a global environment setting "lxc-ubuntu-cloudimage-query-url:"
Its also something we'll want to be aware of as we support LXD, where you can (again) name places where images can be found.
I believe the LXD case is actually much cleaner, but Juju will still want to have a way to expose the LXD configuration.