For Ubuntu 10.04: update gems_dir to true location, update chef version to latest and chef_root to true location

I just set up an ec2 ami on Ubuntu 10.04 and noticed that one of my cookbooks was failing because a path in some file was wrong. After digging through it, I found that my spec for the cookbook was asserting based on the gem_dir set in Fauxhai, but that gem_dir didn't match the actual directory on the Ubuntu instance.