Make an exception in vm.start() actually interrupt the test. The
asyncio.wait() returns list of completed tasks, where exception may be
stored - but is not raised directly. Change to asyncio.gather() that will
propagate the exception by default.
As a side effect, avoid deprecated direct coroutine passing to
asyncio.wait(). This functionality in asyncio.gather() is not
deprecated.
Help debugging test failures by collecting detailed information on
failure. It will be logger to the standard logger, which will end up
either on stderr or in journalctl.
