Random pins

I keep forgetting this when setting up a new yubikey,

mgmt=`dd if=/dev/random bs=1 count=24 2>/dev/null | hexdump -v -e '/1 "%02X"'`
puk="$(< /dev/random tr -dc 0-9 | head -c8)"
pin="$(< /dev/random tr -dc 0-9 | head -c6)"