Add 'show_ip' option to lease command

This needs a refactor (and possibly a new server-side API method?), but it adds what I think is a very valuable method:

When executing `c66 lease`, you can now add the `-a` option to receive the following:

```
76.102.141.241 is allowed to connect to dobt-adopta during 20 minute(s).
For reference, here's the IP address for your first Rails server: 198.199.119.119
```

The `lease` command was great, but it's a pain to go to the c66 website to get my server IP address afterwards.