tests/vm: Display remaining seconds to wait for a VM to start

    def wait_ssh(self, seconds=300):

        starttime = datetime.datetime.now()

        endtime = starttime + datetime.timedelta(seconds=seconds)

        guest_up = False

        while (datetime.datetime.now() - starttime).total_seconds() < seconds:

        while datetime.datetime.now() < endtime:

            if self.ssh("exit 0") == 0:

                guest_up = True

                break

            seconds = (endtime - datetime.datetime.now()).total_seconds()

            logging.debug("%ds before timeout", seconds)

            time.sleep(1)

        if not guest_up:

            raise Exception("Timeout while waiting for guest ssh")