[U-Boot] test/py - test OS boot

Hi Stephen and Simon,

have you thought how to use test/py for testing OS boot? I am not experienced with python to quickly hack it myself but in general I think we should support boot till OS (to test OS handoff, legacy, fit formats, bootm subcommands, go, etc) till certain point and then do reset and if that pattern is found test should pass. I was trying to find out a way how to perform reset command and let test pass. Is there any way how to do it?

Thanks, Michal