Allow attribute used in wildcard FQDN to be customized

In Ubuntu 14.04 `node.name` is returning the FQND, so every time you ran chef the FQND would grow:

```
Run #1: foo.bar.com
Run #2: foo.bar.com.bar.com
Run #3: foo.bar.com.bar.com.bar.com
```

This lets you use `hostname` which gives you the correct value to sub.