API of os-autoinst supports wait_serial command that waits until given regex is shown in serial console. I think that it would be better to use this kind of behaviour than what are we doing currently (needles of console screen). See this code for inspiration.

At the same time, test it thoroughly - for example, isn't it possible that output will be shown sooner than wait_serial gets called? Or isn't it possible that wait_serial regex matches something different (for example, output from previous call)?