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: I8ffb63ba3409c7595a0f13b5ec93c87b1d534d02
Closes-Bug: 1338777
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>
Merge git://github.com/puppetlabs/puppetlabs-nova