add a base_update_cli test
    
    Summary:
    this uses a couple of test repos with fake packages to test the
    basic dnf mechanisms are working, then messes around with the
    python3-kickstart package a bit to try and test the default repo
    configuration is working, keys are in place and so on. We use
    python3-kickstart because we should be able to rely on the copy
    of that package in the 'stable' repo being installable (or else
    the compose would have failed), but it shouldn't be vital to
    the operation of the system.
    
    Test Plan: Run the test, see if it works.
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D1006