py3: open temporary ldif file in text mode
    
    ldif parser uses file in text mode, so we have to open it in text mode
    in py3
    
    Also values passed to parser should be bytes
    
    https://fedorahosted.org/freeipa/ticket/4985
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>