Print warnings and errors to stderr
Don't set the vrf field of DynamicInterfaces

It'll be gone in a few commits anyway.
Move Vrf deletion to dhcp_migrate

...since that's the only place we'll create Vrfs
Re-order migrations so ifaces can validate range
Delete lots of migrations

... in preparation for creating new initial migrations
Remove iface vrf fields; add initial migrations
Add ORM freeze thing to SystemKeyValue migration