[COOK-3685] Add pgdg yum repo attributes for 9.3/9.2 releases

- Add pgdg yum repo attributes for rhel based systems for 9.3
- Enhance pgdg yum repo attributes for newer 9.2 packages

Further information can be found here:  http://yum.postgresql.org/repopackages.php#pg93
In reference to this ticket: https://tickets.opscode.com/browse/COOK-3685