Functionally test downloader concurrency restriction
Pulp's plugin API downloaders all have a concurrency restriction feature in them such that if you configure the
Remote.downloader_concurrency attribute to 5, you should have only 5 downloads interacting with that remote at any given time.
To verify this I think we should use an aiohttp server that listens for 6 connections and then the test schedules like 20 downloads, and the server asserts that only 5 were in flight at a time.
This would use https://aiohttp.readthedocs.io/en/stable/web.html