scripts/pythondistdeps: Do anything only when called as a main script
    
    Note that the code is completely unchanged except for the indentation
    under the new if __name__ == "__main__":
    
    Note that this change is necessary, but not sufficient to use the
    RpmVersion class.
    The init of the RpmVersion class will fail when called from an outside
    script, because the `parse_version()` function is lazily imported from
    the code outside the class.  However, adding the import of
    parse_version() to RpmVersion class is not done right now, because while
    we would import it from `pkg_resources`, other scripts might want to
    rely instead of the lightweight `packaging` module for the import. Thus
    I'm leaving this conondrum to be addressed in the future.