Improve error handling on startup

[iMicknl]

We now raise ConfigEntryNotReady on some exceptions, to make it retry. Not 100% sure if this will work for too_many_requests as well.

2020-09-29 23:59:35 ERROR (MainThread) [custom_components.tahoma] too_many_requests
2020-09-29 23:59:35 WARNING (MainThread) [homeassistant.config_entries] Config entry for tahoma not ready yet. Retrying in 20 seconds
2020-09-29 23:59:56 ERROR (MainThread) [custom_components.tahoma] too_many_requests
2020-09-29 23:59:56 WARNING (MainThread) [homeassistant.config_entries] Config entry for tahoma not ready yet. Retrying in 40 seconds
2020-09-30 00:00:36 ERROR (MainThread) [custom_components.tahoma] too_many_requests
2020-09-30 00:00:36 WARNING (MainThread) [homeassistant.config_entries] Config entry for tahoma not ready yet. Retrying in 80 seconds

[tetienne]

Why create 2 variables? We only use them once.

[iMicknl]

I want to have those two API calls in the try, catch {} as well, however I don't want to duplicate the exception logic 3 times. This was the only solution I could think of.

[tetienne]

But you don't use them in your except blocks. Or perhaps you suggest that these exceptions can happen when we retrieve the devices and scenarios?

[iMicknl]

Yes, these exceptions can happen on retrieval of the devices and scenarios. They are needed later on in the init, however this won't be reached in case of any errors.

See #277.