- Removed hardcoded yum repository configuration in favor of
  commands dynamically generated based on repo-url and repo-file
  arguments. We maintain a sane default set of repositories.
- Added generic rpm_setup_config parameter to add support for
  installing .rpm or .repo files before building containers.

Co-Authored-By: Ryan Hallisey <rhallise@redhat.com>
Implements: blueprint custom-repos
Change-Id: I1b3a7647a9e7239de3cd162cb6f464f05632bde1