Add option to act on forward-call failure: call another coco endpoint specifying single host

For scheduling a coco endpoint that calls status (#44 ) and restarts every node that doesn't respond with `running: True`, config options to define that behaviour is needed and the functionality needs to be added to `Endpoint.call()`. The config in the endpoint config could look like:
```
call:
forward:
:
on_failure:
call_single_host: restart
reply:
running:
value: True
```
This will call restart for every node that failed for the conditions specified with `reply: running: value: True`.

This is similar to #78 and should be added to that functionality afterwards.

**Depends on:**
- functionality to pass single host to endpoint call: #76
- functionality to test the values in a reply: #77