Check socket or stats URL

Options are backwards compatible.

```
firewall1.dev:~# ruby check-haproxy.rb -S 127.0.0.1 -P 8000 -q haproxy_stats -u monitor -p secret -e -s be_api
CheckHAProxy OK: UP: 100% of 1 /be_api/ services

firewall1.dev:~# ruby check-haproxy.rb -S /var/run/haproxy/admin.sock -e -s be_api
CheckHAProxy OK: UP: 100% of 1 /be_api/ services
```

Cheers!
Daniel