[Enhancement] move compatible OVAL checks to the shared directory

- Move compatible Fedora checks to the shared directory
- Share no_netrc_files OVAL check and enable for RHEL 6 & 7 and Fedora
- Share securetty OVAL checks and enable for RHEL 6 & 7 and Fedora
- Add Fedora 20 OVAL check
Merge pull request #337 from redhatrises/shared_fedora_updates

[Enhancement] move compatible OVAL checks to the shared directory