otptoken-add: improve the robustness of QR code printing
    
    The python-qrcode print_ascii() method does not work in terminals with
    non-UTF-8 encoding. When this is the case do not render QR code but print a
    warning instead. Also print a warning when the QR code size is greater that
    terminal width if the output is a tty.
    
    https://fedorahosted.org/freeipa/ticket/5700
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>