The return code on the end maintenance API call does not correspond with the info provided in the documentation

[ajoaoff]

Original issue opened by @ArturoQuintana at kytos#35.

@hdiogenes @ajoaoff @rmotitsuki

It has been tested the API call /maintenance/{mw_id}/end on PATCH with the idea to execute an early end over a maintenance task that is running. Unfortunately, this task does not succeed.
The test code used is as follow:

def test_040_end_mw_on_switch(self):
        # Setup maintenance window data
        start = datetime.now() + timedelta(seconds=60)
        end = start + timedelta(hours=1)
        payload = {
            "description": "mw for test 040",
            "start": start.strftime(TIME_FMT),
            "end": end.strftime(TIME_FMT),
            "items": [
                "00:00:00:00:00:00:00:02"
            ]
        }

        # Request maintenance schema creation, and extract the mw_id
        json_data = self.request_maintenance(payload, False)
        mw_id = json_data["mw_id"]

        time.sleep(10)

        api_url = KYTOS_API + '/maintenance/' + mw_id + '/end'
        request = requests.patch(api_url)
        assert request.status_code == 201`
```

[ajoaoff]

Closed by #24