Regression fix: rule table with ext. member support doesn't offer any items
    
    There is a JS error.
    
    Rule tables with external member has more than one column and therefore exclude parameter for adder dialog is not array of strings but array of objects. normalize_values function can't work with it and causes JS error.
    
    This patch creates proper exclude array before passing it to adder dialog.
    
    https://fedorahosted.org/freeipa/ticket/3711