This implements the new model infix-if-vlan.
The new CLI is:
root@infix-00-00-00:/config/interfaces/interface/vlan10/> set vlan id 10 lower-layer-if eth0
with an possible extra option for tag-type, default tag-type is c-vlan.
Create topology objects that are tailored to represent topologies on
the expected format. This let's us make convenient accessors for
things like the controller node, infix devices, getting the ports used
to reach a certain device from another one, etc.
