Convert zeroconf integration to use python-zeroconf

[balloob]

We migrated the zeroconf integration to use aiozeroconf. However, @amelchio notified us that asyncio.create_datagram_endpoint is not supported on Windows. So we need to migrate back to using python-zeroconf, which does work.

CC @Kane610

[elupus]

https://bugs.python.org/issue29883 issue holding implementation fix for this possibly for python 3.8, not that it helps us unless we can monkey patch it in.

[Jc2k]

Before we revert anything...

It looks to me like create_datagram_endpoint is one of the pieces the event loop is supposed to provide. On Windows, the Proactor event loop does not support UDP at all. But the docs say its a proactor problem, they don't say its a Selector event loop problem. uvloop also does not support UDP for Windows at all.

If we want to move towards native asyncio integrations as gold standard AND support Windows, is it more appropriate to reconsider uvloop on Windows? Is it better to build on an event loop that supports UDP or on one thats a bit faster but is incomplete? Would this probably go away if we used the stock event loop on Windows?

[Jc2k]

Arrgh its super lame that the other event loop doesn't support subprocesses.

[balloob]

My bad for not writing down why alternatives won't work, but it looks like you figured it out.

Given the Python release schedule, we can expect Python 3.9 in either 2020 or 2021. When that happens, we will adopt Python 3.8 as our minimum version and can migrate back…

[balloob]

Just for other readers:

Event loop	Windows Caveat
Proactor	No UDP
Selector	No subprocess
UVLoop	No Windows build available

[pvizeli]

We need Proactor event loop on windows because we have more as 512 current coroutines because we have a lot of async functions they are awaited. That was the reason why we move over to this on windows initial.

[balloob]

Python 3.8 contains a new event loop https://twitter.com/VictorStinner/status/1133323227298697216