Install bzip2 on RHEL 7

cc @opscode-cookbooks/release-engineers 
To keep things simple I think we should just install this on anything rhel:

```ruby
package 'bzip2' if rhel?
```

Package installs are idempotent so it shouldn't hurt if the package is already installed. Let's also add a comment on why we have to install it (e.g. it's a dep of ruby-isntall?).