The SalLogHandler is issues a large number "coroutine not awaited" messages after running unit tests. We think this is because logging is synchronous but SalLogHandler writes asynchronously, so it has to create a coroutine for each message it emits, and the fact that it uses asyncio.run_coroutine_threadsafe to do this, so that logging can be done from background threads.

Try to fix this by keeping track of unfinished concurrent.futures.Futures returned by asyncio.run_coroutine_threadsafe and closing them in the close method of SalLogHandler.