VLAN interfaces should have device autodetected

[Dan Sneddon]

VLAN interfaces can be created by stating the parent device in the VLAN definition, but the device should be applied automatically if the VLAN is a member of an interface.

For instance, this works:

-
  type: interface
  name: nic2
  addresses:
    - ip_netmask: 192.168.20.10/24
-
  type: vlan
  vlan_id: 20
  device: nic2

But the device: nic2 shouldn't be required. It would be better if type interface accepted a members: stanza, and the VLAN could be a member. The device could be determined by the parent object (interface in this case).