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 
```
core@localhost ~ $ sudo find / -name "yy-vmware.network"
/usr/lib64/systemd/network/yy-vmware.network
```

I think I should put yy-vmware.network into /etc/systemd/network.