Support host interfaces

http://ci.wakame.jp/job/wakame-vnet.integration-test/171/

Host ports now require interfaces to be created:

```
  - uuid: if-dp1eth0
    mode: host
    port_name: eth0
    owner_datapath_uuid: dp-1
    network_uuid: nw-public
    mac_address: "02:01:00:00:00:01"
    ipv4_address: <%= dp1_ipv4_address %>
```