* Simplify list of required packages (and add `grubby`).
* Move Disabled -> Enforcing steps from `changing-to-enforcing-mode` to
`enabling-selinux`.
* In `changing-to-enforcing-mode`, use the correct procedure based on
whether SELinux is currently Permissive or Disabled.
* Add step for ensuring that filesystem is relabeled when re-enabling
SELinux.
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>