Add NFS client for vagrant synced folder

I created a vagrant box based on boot2docker v0.6.0 to support NFS synced folder,
https://github.com/YungSang/boot2docker-vagrant-box/releases/tag/yungsang%2Fv0.6.0-nfs

but this PR would be better and faster than installing NFS client on boot in the box.

I'd be glad if it would be helpful for other cases, too.