reformat streelight code based on [#18]

[chicco785]

lego-diorama-usi-2022/traffic/street_lights_client.py

Line 58 in c853492

def on_message(client, userdata, msg):

the flow should be:

1. subscribe to command topic
2. when command received to turn on light (e.g. { "light": { "power": "on" } }):
   1. turn on lights (a leave them on - the off control will be done with an external logic that ask to turn off)
   2. send ack to cmdexe topic (e.g. { "light": { "power": "ok" } })
   3. update status attribute on attrs topic (e.g. { "powerState": "on" })
3. when command received to turn off light (e.g. { "light": { "power": "off" } }):
4. turn off lights
5. send ack to cmdexe topic (e.g. { "light": { "power": "ok" } })
6. update status attribute on attrs topic (e.g. { "powerState": "off" })