VM Builders: Shutdown Command in Examples

This adds the shutdown command to the vmware and virtualbox configuration examples. I suggest this because of a [recent mailing list thread](https://groups.google.com/forum/#!topic/packer-tool/7a9GDPad0lo) on the subject. Hopefully seeing it in the example will bring it to attention and avoid similar issues.

I also noticed that the website won't start with Ruby `2.0.0`, so I specified `1.9.3` in the Gemfile.