pass disconnect properties to on_disconnect handler

[miketrebilcock]

on_disconnect_handler does not pass through the parameters from paho. I need to check the rc parameter to understand the reason for disconnect.

[Sohaib90]

@miketrebilcock can you provide a little more context to this PR. Why is it required? What did you do to fix the issue? Which tests refer to the change you propose in this PR. Thanks :)

[miketrebilcock]

I was having issues with connections where the server was forceable disconnecting the client. It was passing messages to indicate why the connection was being disconnected, by the library was passing them through to my code. This PR ensures that any data passed in the disconnect is accessible to code that is using the library.

I noticed that some extra commits have managed to be added to the PR, I'll update it to remove them.

[Sohaib90]

@miketrebilcock can you add some tests to ensure that the changes you have proposed actually work?

[howroyd]

Massive +1 to this PR please.

To add use case as mentioned:
The userdata passed into the callbacks in my case has condition variables (threading.Event) to signal an "is_connected" state (rather than using globals.) I can set this variable in on_connect because the userdata structure is passed through, but I cannot clear on_disconnect.

e.g.:

@dataclasses.dataclass
class Userdata:
   connected: mp.Event = dataclasses.field(default_factory=lambda: mp.Event())

@mqtt.on_connect()
def on_connect(client, userdata: Userdata, flags, rc):
    if 0 == rc:
        userdata.connected.set()

@mqtt.on_disconnect()
def on_disconnect(client, userdata: Userdata, rc):  # <- this doesn't work because the args aren't forwarded
    userdata.connected.clear()

[miketrebilcock]

I'll try and get the tests added this week so that it can be merged.