use assert_script_run when possible
    
    Summary:
    D637 / ec6b3ff4 switched from using needle matches to using
    validate_script_output when we want to run a console command
    and check the result. validate_script_output is kinda over-
    powered when all you want to do is check the command succeeded
    (returned 0), though. testapi provides assert_script_run for
    doing exactly that - it runs a script and fails if the script
    fails (returns anything but 0). This gives us cleaner code and
    is slightly more robust; validate_script_output uses the mini
    web server on the worker, which I've occasionally seen crap
    out, so it seems good to avoid using it when possible. assert_
    script_run doesn't need it.
    
    Test Plan: Check all (affected) tests still work properly.
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: jskladan, garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D714