Python API: coroutine return value should not be discarded

Build 3.3.20191018-nightly

I'm writing a CLI that needs to exit with a custom value on some business logic condition. It's probably ok to let iterm2 handle connection errors.

I can't return my own value from iterm2.run_* functions or raise an exception that I can gracefully catch without any other printout, I can't sys.exit from my coroutine without triggering the default error handling, I can't use asyncio.run without having a long pause after my coroutine.

Probably as simple as letting the return value of the coroutines passed to iterm2.run_* propagate the way it's done in asyncio.run_*.