Add support for Amazon Linux

This pull request depends on the changes in https://github.com/basho/riak-chef-cookbook/pull/128. It is also a squashed version of https://github.com/basho/riak-chef-cookbook/pull/126 with `.kitchen.cloud.yml`.

Tests can be run using the following commands:

```bash
$ KITCHEN_YAML=.kitchen.cloud.yml kitchen test default-amazon-2014031
$ RIAK_ENTERPRISE_KEY="******" KITCHEN_YAML=.kitchen.cloud.yml kitchen test enterprise-amazon-2014031
```