xmlrpc tests: add test for idrange auto-private-groups option
    
    Scenarii:
    - idrange-add prevents --auto-private-groups with a local id range
    - idrange-mod prevents --auto-private-groups with a local id range
    - auto-private-groups accepts only true/false/hybrid/empty values
    
    Related: https://pagure.io/freeipa/issue/8807
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>