Already saved private key is deleted if trying to provision already provisioned board

[jesperbnp]

This check deletes the previously saved private key if trying to re-provision a board.

rpi-sb-provisioner/service/rpi-sb-provisioner.sh

Line 949 in 170825a

get_variable private-key > "${KEYPAIR_DIR}/${TARGET_DEVICE_SERIAL}.der" || N_ALREADY_PROVISIONED=$?

Suggest changing to something like this:

N_ALREADY_PROVISIONED=0
PRIVATE_KEY=$(get_variable private-key) || N_ALREADY_PROVISIONED=$?
if [ 0 -ne "$N_ALREADY_PROVISIONED" ]; then
    keywriter_log "Warning: Unable to retrieve device private key; already provisioned"
else
    echo ${PRIVATE_KEY} > "${KEYPAIR_DIR}/${TARGET_DEVICE_SERIAL}.der"
fi
get_variable public-key > "${KEYPAIR_DIR}/${TARGET_DEVICE_SERIAL}.pub"