Add haproxy module

I just implement an haproxyctl module which is for sending commands to haproxy stats socket. Some simple usage would be like

```yaml
- name: disable foobar server
  haproxyctl: state=disabled name="foo/bar-001"
```

or you can query info by

```yaml
- name: disable foobar server
  haproxyctl: state=info
  register: haproxy_info
```

and you get

```json
{"changed": false, "failed": false, "msg": "Command show info executed", "result": {"CurrConns": "1", "Maxconn": "2000", "Maxpipes": "0", "Maxsock": "4015", "Memmax_MB": "0", "Name": "HAProxy", "Nbproc": "1", "Pid": "12377", "PipesFree": "0", "PipesUsed": "0", "Process_num": "1", "Release_date": "2013/06/17", "Run_queue": "1", "Tasks": "3", "Ulimit-n": "4015", "Uptime": "0d 1h00m45s", "Uptime_sec": "3645", "Version": "1.4.24", "description": "", "node": "foobar.com"}}
```

I made this module only for fitting my own needs, I may continue working on this if I have spare time. And if you see this pull request helps, and you want to continue working on it, you're welcomed to do so.