bootstrap property suppliers should be Supplier<Iterable<Map>>, not Iterable<Supplier>

```
This allows lazy loading of files based on properties already loaded, so that 
we can pick up an <env>.properties file based on an env defined in 
user.properties.
```

Original issue reported on code.google.com by `joe.j.kearney` on 26 Jan 2011 at 10:54
