Address misc pylint issues in CLI scripts
    
    The CLI script files have additional pylint issues that were not noticed
    before. The violations include using dict.keys() without directly
    iterating of the result, inconsistent return statements and set([])
    instead of set literals.
    
    * dict-keys-not-iterating
    * inconsistent-return-statements
    * onsider-using-set-comprehensio
    
    See: https://pagure.io/freeipa/issue/7772
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>