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 
So it's not a bug, it's my mistake. I'm very sorry...
I should use the following unit:

```
#cloud-config

coreos:
  units:
    - name: 00-ens192.network
      content: |
        [Match]
        Name=ens192

        [Network]
        DHCP=v4
        DNS=8.8.8.8
        DNS=8.8.4.4
```