Translate the reason code as `normal_disconnect`
Translate the reason code as `normal_disconnect`

The spec has overlapping meanings for 0 as a reason code depending on
the context: `normal_disconnect`, `success`, `qos 0`...

For disconnects it should be `normal_disconnect` instead of `success`.

erlio/vernemq,erlio/vernemq,erlio/vernemq,erlio/vernemq