(QENG-1206) Acceptance failing when trying to install epel-release...

and EPEL packages from public mirrors
- add ability to set epel_url, epel_arch and epel_package as global
  options or on a per-host basis
- added reasonable default values
Merge pull request #479 from anodelman/epel

(QENG-1206) Acceptance failing when trying to install epel-release...