Adding an "openstack::repo" class which automatically sets up repos

Tested with the following combinations:

- RHEL-alikes, OpenStack Folsom
- RHEL-alikes, OpenStack Grizzly
- Fedora 18, OpenStack Grizzly (F18 includes folsom)
- Ubuntu 12.04+, OpenStack Folsom
- Ubuntu 12.04+, OpenStack Grizzly

Change-Id: I737da83d138695a178aaf3fa711a6e08a678adde
Merge "Adding an "openstack::repo" class which automatically sets up repos"