Help new users if their SELinux is not-upgraded yet.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Merge pull request #8030 from SvenDowideit/add-help-if-selinux-is-out-of-date

Help new users if their SELinux is not-upgraded yet.