Comment 3 for bug 1443942

This PR https://github.com/juju/juju/pull/2190 did not land in time, so the described behavior for 1.24 and 1.25 is not in place and MAAS is still broken when the address-allocation feature flag is enabled. I'll include the changes from #2190 into a PR which forward ports of the fix for bug 1442257. Once it lands, the described behavior (using a state policy instead of the provider type to determine whether to enable NAT, as well as listing all subnets CIDRs in a the default VPC explicitly as separate SNAT rules) still needs improvement. James, please ping me if something is not clear.