Create Is Container Flag

[georgenalen]

There are individual controls that should not be enabled on a container system. There needs to be a broad is_container variable added to have a single point to disable tasks that don't work on container environments.

[jamescassell]

More generically, there are things that don't work without systemd running, which might or might not be a container. Very few things truly don't work in a container. One is SELinux.