bugfix: add two N/A/ columns if an entry does not have any ip address

Append two "N/A" to devices if a device does not have assigned ip addresses. What happens currently is that when a device does not have an ip address, ```ui.list(...)``` displays the first column from the next entry in the last column of the preceeding entry.

For example

```bash
ID          Name        Type        Status      Facility    Public_IP   Private_IP
1           server1     xxxx        xxxxx       xxxxxx                  2
server2     xxxx        xxxx        xxxxx       192....     192....     3
```

This has a cascading effect on the display as all the next columns are shifted.