Automatically reconnect on idle, fixes #34

[tris]

Should be pretty self-explanatory.

Tested locally:

1. Run ecoflow_exporter.py
2. Wait 10 seconds
3. Observe that events are flowing
4. Open EcoFlow mobile app
5. Wait 10 seconds
6. Observe that events are still flowing
7. Close EcoFlow mobile app
8. Wait 10 seconds
9. Observe that events stop (Message queue is empty)
10. Wait 60 seconds
11. Observe that the client reconnects to MQTT
12. Wait 10 seconds
13. Observe that events start flowing again

[berezhinskiy]

@tris Thanks for contributing. I believe the MQTT_TIMEOUT environment variable will be beneficial. I'll investigate the issue with the CI Docker build.