Arthur/ssh check

Check meant to:
1. Check the status of SFTP
2.Check The response time 


@LeoCavaille 
You shouldn't unpack the conf like that. It defeats the purpose of using a namedtuple.

You should do:

```python
conf = self._load_conf(instance)
```

and then if you want to get the host you can just get it using:
```python
conf.host
```