Fixes Facts string comparisons in CentOS 7

- CentOS Project has adopted a new rule for versioning numbers. The major number
  matches the RHEL major number, but the minor number is generated from the
  release date. For example, CentOS 7.1407.
- Adds support for Scientific Linux.

Change-Id: I183dd8e0a019d5fb486e8f0641f6ab81ae758f8f
Closes-Bug: 1338777
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>