* Simplify docker systemd unit
systemd handles missing unit by ignoring the dependency so we don't need
to template them.
* Remove RHEL 7/CentOS 7 support
- remove ref in kubespray roles
- move CI from centos 7 to 8
- remove docs related to centos7
* Remove container-storage-setup
Only used for RHEL 7 and CentOS 7
Some packages requirements depends on inventory variables
(`kube_proxy_mode` in that case but it could apply to others).
As the case seems pretty rare, instead of adding complexity to pkgs, we
add an escape hatch to use jinja conditions.
That should be revisited if we find ourselves shoehorning lots of logic
in this later on.
Uses the logic introduced in the previous patch to convert all
kubernetes/preinstall/vars/* os specific files to the `pkgs`
dictionary.
Some niceties for devs:
- always validate the `pkgs` variable to catch mistakes in CI.
- ensure that `pkgs` is always sorted. This makes it easier to find the
packages you're looking for.
Max Gautier