Add MQTT gateway for MySensors

[MartinHjelmare]

Description:

• Use mqtt component to enable a MySensors MQTT gateway.
• Setup the MQTT gateway if mysensors config has mqtt as a value for
  the key device in the list of gateways.
• Simplify two lines in the mqtt component.

I will add voluptuous config validation in a separate PR, after this is merged.

Pull request in home-assistant.io with documentation (if applicable):
home-assistant/home-assistant.io#841

Example entry for configuration.yaml (if applicable):

mqtt:
  client_id: home-assistant-1
  keepalive: 60

mysensors:
  gateways:
    - device: mqtt
      persistence_file: '~/.homeassistant/mysensors.json'
      topic_in_prefix: 'mygateway1-out'
      topic_out_prefix: 'mygateway1-in'
  debug: true
  persistence: false
  version: 2.0
  optimistic: false
  retain: true

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If code communicates with devices, web services, or a:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass

[omgapuppy]

@MartinHjelmare out of interest, does this include support for the MySensors API 2.0 i.e the new / deprecated variables as per their dev doc?

[turbokongen]

Maybe use constant for 'mqtt' ?

[balloob]

This is actually the more appropriate way as it allows people to overwrite the built-in mqtt component

[MartinHjelmare]

I think @turbokongen means that I should extract mqtt into a constant, ie

MQTT_COMPONENT = 'mqtt'

I think that doesn't hurt right?

[turbokongen]

@MartinHjelmare you got it right 👍

[MartinHjelmare]

@omgapuppy No, we need to add the new S and V_TYPES to the appropriate sensor platforms in home assistant. That's another PR. All new types are already supported in the pymysensors library. So it's just a matter of sorting them into the correct platform, that makes sense. Help is welcome.

[Landrash]

@MartinHjelmare I'll give it a try today to map the new types to the appropriate platform. Ok if I work against your fork of HA?

[MartinHjelmare]

@Landrash That would be awesome! Yes, you can work against my fork. Should I create a new branch there, so you can do a PR to that?

[Landrash]

@MartinHjelmare Yes, sounds like a plan!

[MartinHjelmare]

I've pushed a new branch to my fork based off dev branch:
https://github.com/MartinHjelmare/home-assistant/tree/mysensors-add-new-types

Let me know if you want me to do something else.

[MartinHjelmare]

This should be good for merging now.