Add test for client installation with empty keytab file
    
    Missing test case for cf1301fb064fc230c780c4bc5eeccb723899f7b6.
    
    https://pagure.io/freeipa/issue/7625
    
    Signed-off-by: Armando Neto <abiagion@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>