This commit mainly adds support for Fedora 21, which now has packages in
imeyer's Package Cloud repository.

- Update centos base boxes to latest releases
- Add ubuntu 14.04
- Add fedora to 'rhel' conditionals where applicable
- Register the 'runit_service' resource with MiniTest::Chef so it can be
  asserted using the runit state instead of underlying system service
  state checking because that generally will attempt to use the "lsb
  init interface," which doesn't work with systemd