Comment 8 for bug 1513529

So to fix the specific issue that was blocking juju and MAAS, -backports has been enabled in precise and trusty images.

yakkety images will have the same sources.list as in the server installation (albeit via a one-time sync).

As xenial has been released with a difference between the sources.lists and there isn't a currently compelling reason to modify it under users, we won't make the change there. If, in the future, there is a specific reason to revisit this decision, we will be happy to do so then.