[bugfix] Migrate grub to grub2 for RHEL7 and Fedora

- Migrates grub settings to grub2
- Enables grub2 OVAL checks for Fedora and RHEL7
- Add superuser check to grub bootloader OVAL check
- Update XCCDF to reflect grub2 settings
- Enable grub2 checks in rht-cpp profile
- Update grub2 OVAL permission checks
- Fixes #54
- Fixes #55
- Fixes #56
- Fixes #57