Add yum/arch support

Adds the 64bit yum repo if a 64bit OS is detected. (#13)
This is based off of how [chef-mongodb](https://github.com/edelight/chef-mongodb/blob/fd7ab07ebfd54fc1049bc37367b92842f37310ac/recipes/mongodb_org_repo.rb#L41) does it, and adds yum as a cookbook dependency.

Updated the tests for RHEL to be similar to the Debian tests.