puppet-timezone: Added support for CentOS and AWS Linux.

Hi,

I added support for CentOS and AWS Linux. I tested it on both OS as well.

CentOS:
![image](https://f.cloud.github.com/assets/2142512/482194/6378e7b8-b88c-11e2-9f45-5607c2069bef.png)

AWS Linux:
![image](https://f.cloud.github.com/assets/2142512/482202/b9621320-b88c-11e2-91ed-3c00febee130.png)