os-autoinst implements script_run itself now, we aren't
required to implement it ourselves any more. os-autoinst's
implementation is better than ours, as it allows for verifying
the script actually ran (via the redirect-output-to-serial-
console trick).
So this drops our implementation so we'll just use the upstream
one. Where I judged we don't want to bother with the 'check
the command actually ran' feature I've adjusted our direct
script_run calls to pass a wait time of 0, which skips the
'wait for command to run' stuff entirely and just does a simple
'type the string and hit enter'.
Because of how the inheritance works, our assert_script_run
calls already used the os-autoinst script_run, rather than
the one from our distribution.
This should prevent prepare_test_packages sometimes going
wrong right after removing the python3-kickstart package, as
we'll properly wait for that removal to complete now (before
we weren't, we'd just start typing the next command while it
was still running, which could result in lost keypresses).