Refactor

- use an helper
- use yum cookbook
- use URI to create url
- Fix problem with "name" resource != new_resource.name
- Add a default value for `type`

Based on #2
- We are planning on removing the dependency to `apt` soon, as well, and managing the files ourselves so we can get the exact behavior we want.
- Chef provides a `repo_gpgcheck` in the `[global]` section, but we want to specifically enable it for our yum repository, regardless of what options are set for other repos. 
- The code above here is also important for regenerating the repo metadata (the `makecache` command).