Set uWSGI to listen on socket by default

If you set `web_server` to anything but `"apache"`, the
default settings broke and rose a

```
Chef::Log.error!("uwsgi cannot bind to ports less than 1024. Please set \"node[graphite][listen_port]\" to an appropriate value")
```

This setting fixes the default behavior for uWSGI without
altering the default behavior for Apache.

This should fix hw-cookbooks/graphite#139 as well.