Fix hdmi_cec entity race

[yottatsa]

Update shouldn't be called before adding the entity.

Description:

1. update() is moved outside of the __init__(), otherwise it triggers entity creation with entity_platform.async_add_entities, see f241bec.
2. add_entities is now updating those entities instead.
3. Callback is now registered with async_added_to_hass.
4. Callback is only schedules update with self.schedule_update_ha_state(True).
5. Added transitional states.

Related issue: fixes #12846

Example entry for configuration.yaml:

hdmi_cec:

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

[homeassistant]

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Once you do that we will be able to review and accept this pull request.

Thanks!

[yottatsa]

@MartinHjelmare addressed. Now I'm using add_entities(entities, True), and self.schedule_update_ha_state(True) is in the proper place.

[yottatsa]

@MartinHjelmare addressed. async_schedule_update_ha_state is used now.

[MartinHjelmare]

Thanks!

For future PRs please don't squash commits after review has started to make it easier for readers to track changes. We always squash when we merge anyway.

Can be merged when build passes.

[heisenberg2980]

Has this issue being fixed? I am still having the same problem

2020-03-06 12:06:10 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/entity_platform.py", line 425, in _async_add_entity
    raise HomeAssistantError(msg)
homeassistant.exceptions.HomeAssistantError: Entity id already exists: switch.hdmi_2