Fix windows OSError: [WinError 10022] An invalid argument was supplie…

[darindf]

This solves the issue #342 of running multiple workers on Windows.

Specifically it avoid the sock.listen issue by closing the socket in the worker, and then letting asyncio.create_server reopen the socket using the same host, port and other configuration information from the inherited socket from the parent.

INFO: Started server process [36716]
INFO: Waiting for application startup.
Process Process-8:
Traceback (most recent call last):
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\multiprocessing\process.py", line 297, in _bootstrap
    self.run()
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\multiprocessing\process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\site-packages\uvicorn\main.py", line 307, in run
    loop.run_until_complete(self.serve(sockets=sockets))
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\asyncio\base_events.py", line 584, in run_until_complete
    return future.result()
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\site-packages\uvicorn\main.py", line 322, in serve
    await self.startup(sockets=sockets)
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\site-packages\uvicorn\main.py", line 349, in startup
    create_protocol, sock=sock, ssl=config.ssl
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\asyncio\base_events.py", line 1397, in create_server
    server._start_serving()
  File "c:\ProgramData\anaconda3\envs\py37.test\lib\asyncio\base_events.py", line 287, in _start_serving
    sock.listen(self._backlog)
OSError: [WinError 10022] An invalid argument was supplied
INFO: Started server process [41732]

[gvbgduh]

Should it be nt?
There's also a handy built-in lib - https://docs.python.org/3.7/library/platform.html#platform.system for that.
So, platform.system() == "Windows" might be a bit better choice.

[gvbgduh]

There're also some failing tests, including against Windows.

[gvbgduh]

Some failing tests and a few comments.