First pass fixing tests that raise exceptions caught by asyncio.gather

[balloob]

So I realized that we use asyncio.wait at a bunch of places without checking the result. The problem of asyncio.wait is that any exception is lost and cannot be attributed to a certain place. This is bad.

So we should start exchanging asyncio.wait with asyncio.gather, so that exceptions can propagate. Each time we do this, we will catch bugs and tests that were raising during teardown (which is also some flaky tests!)

This PR is a bunch of fixes required for letting tests pass after we start using asyncio.gather inside hass.async_block_till_done .

Eventually I want to phase out the using of asyncio.wait without checking the return values.

Test failures in this pass were caused, among other things by:

• unmocked attributes being written to storage, crashing the JSON serializer
• missing persistent_notification.create service

[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as its been labeled with a integration (demo) you are listed as a codeowner for? Thanks!

[elupus]

Looks good. I suspect we'll start finding a bunch of cancelleded exception on shutdown.