Cache the last-transmitted SCEP nonce value
    
    Instead of clearing SCEP values, cache the old nonce, and don't pass
    them along to the helper if they're being re-used.  This lets the
    SCEP-data-not-supplied path play out and cause new data to be generated,
    while leaving the last-used data in the data file in case we need it for
    troubleshooting.