Added rewrite-host-header to system model

Also, this doesnt converge.  I believe instead of:

```
default['repose']['cluster_ids'] = [
  {
    "id": "repose",
    "rewrite_host_header": "true"
  }
]
```

... that you want the following:

```
default['repose']['cluster_ids'] = [
  {
    'id' => 'repose',
    'rewrite_host_header' => 'true'
  }
]
```