py3: ipautil: open tempfiles in text mode
    
    Code in ipautlis works with text, so tempfiles should be open in
    textmode otherwise TypeErrors are raised
    
    https://fedorahosted.org/freeipa/ticket/4985
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>