cleanup on asyncio.CancelledError

[NovapaX]

I'm putting some api calls in a async_timeout, because aiocoap has a 1+ minute timeout by default.

But pytradfri doesn't cleanup on a asyncio.CancelledError.
I think it should.

The place to add such thing would be here right?
https://github.com/ggravlingen/pytradfri/blob/b4a0ee2210d6a5643bffc40829e6f093a1dbc796/pytradfri/api/aiocoap_api.py#L99-L102

        except asyncio.CancelledError as e:
            yield from self._reset_protocol(e)
            raise e

If so I would be glad to make a pull request.

[lwis]

That's fine, async_timeout would be handy as the Gateway should respond in less than a minute.

[NovapaX]

Putting things in a async_timout can also be used as a workaround for some aiocoap issues.
(for example not properly cancelling the exchange on a fatal DTLS error. Instead is lets the exchange timeout while outputting a lot of error messages.)