Clearer error on connection refused

[bestouff]

When the connection to the broker fails, rumqtt logs:

ERROR 2019-04-29T13:16:50Z: rumqtt::client::connection: Connection error = Error(Inner(MqttConnectionRefused(5)))

In this case, I would have liked to see "not authorised" or something like that in the logs. Maybe it's the signification of the 5 I see, but would it be possible to make it clearer ?

[bestouff]

I see this now:

ERROR 2019-05-28T08:02:03Z: rumqtt::client::connection: Connection error = Error(Inner(Io(Custom { kind: Other, error: StringError("failed to lookup address information: Name or service not known") })))

... which is fine with me. Is it fixed in all cases ?

[tekjar]

In this case, I would have liked to see "not authorised"

I thinks this will be an improvement but we can easily check the mqtt return code spec for now