[virtual box] ubuntu server shared folder

1. Install Virtualbox Guest Additions
http://en.ig.ma/notebook/2012/virtualbox-guest-additions-on-ubuntu-server


2. share folder as client version
https://sites.google.com/site/waue0920/Home/linux-bi-ji/virtualbox-client-duan-ruo-shilinux-yong-gong-yong-zi-liao-jia-de-she-ding-fang-fa