Test run_forever and run_until_complete return values

[hosaka]

Even though asyncio run_forever() returns None, historically, since quamash qasync returns QApplication exit code. This adds a test for that, as well as testing run_until_complete() returning future result as per asyncio docs.

[hosaka]

Was a bit too hasty resolving a merge conflict in #140 and accidentally removed test_qeventloop_in_qthread test, adding it back here.