Add Sonos device attribute with grouping information

[amelchio]

Description:

This PR replaces the Sonos is_coordinator boolean attribute with a more useful attribute sonos_group that reveals the actual speaker group arrangement.

Related issue (if applicable): suggested in forum

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.github.io#<home-assistant.github.io PR number goes here>

BREAKING CHANGE NOTE: The media_player.sonos attribute is_coordinator has been removed; the new attribute sonos_group (listing all group members, coordinator first) can be used instead.

Example template:

This will list the players that used to have is_coordinator == True:

{% for player in states.media_player -%}
{% if player.attributes.sonos_group | first == player.entity_id -%}
{{ player.entity_id }}
{% endif -%}
{% endfor -%}

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox.

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

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

[pvizeli]

I think we should implement the group/snapshot feature on core to generalize the handling

[amelchio]

Okay ... and what do you think about this PR? 😃

[balloob]

So I'm fine with storing this in the state machine. I am a bit confused as to why we would make it more difficult to find who is the coordinator? Isn't it that we can only send commands to the coordinator?

[amelchio]

Sending commands to slaves works without this, the platform will redirect the command to the coordinator.

The attribute in this PR was hashed out in this forum thread after the original solution with is_coordinator turned out to not provide enough information for the intended use (building a UI for groups).

I think it is okay to be a bit verbose because it is not used much.