Modified: Added scripts/chef.sh. (install Chef-client)

**Install Chef-client**

Reference of [Packerを使ってVagrantのBoxを作る方法を一つずつ説明する](http://niku.name/articles/Packer%E3%82%92%E4%BD%BF%E3%81%A3%E3%81%A6Vagrant%E3%81%AEBox%E3%82%92%E4%BD%9C%E3%82%8B%E6%96%B9%E6%B3%95%E3%82%92%E4%B8%80%E3%81%A4%E3%81%9A%E3%81%A4%E8%AA%AC%E6%98%8E%E3%81%99%E3%82%8B/index)