add(coreos-base/oem-niftycloud): added initial oem for niftycloud

These are the initial oem scripts for niftycloud.
NIFTY Cloud is one of the most popular public cloud service in Japan.

cc: @kelseyhightower 
You could simplify this script by replacing a chunk of this with:

```sh
${VMTOOLSD} --cmd 'info-get guestinfo.user_data' | openssl enc -d -base64 > "${TMPFILE}"
if [[ -s "${TMPFILE}" ]]; then
    coreos-cloudinit --from-file="${TMPFILE}"
else
    echo "guestinfo.user_data undefined." >&2
    exit 1
fi