stahnma/puppet-module-epel: Added support for Amazon's AWS Linux

Hi,

Good day to you. 

I added support for Amazon's AWS Linux by enabling the already installed EPEL repo. All AWS Linux comes with a disabled EPEL repo, so changes to the module was minimal.

http://aws.amazon.com/amazon-linux-ami/faqs/#epel

My test:
![image](https://f.cloud.github.com/assets/2142512/487487/3bc9ccfc-b95c-11e2-81ba-0d9fb8215073.png)

Thanks.