Properly convert DN in ipa-client-install
    
    ipa-client-install crashed when IPA server anonymous access was
    disabled and base DN was thus generated via realm_to_suffix
    function which, however, returns a DN object and not string.
    
    DN was converted to string, ipa-client-install no longer crashes
    in this scenario.
    
    https://fedorahosted.org/freeipa/ticket/3088