python: add CGroups v1 support
python: add CGroups v1 support

For RHEL 8 we still need to support CGroups v1, this was tested seperate
of the cockpit-bridge as the bridge currently does not run on Python 3.6
due to the usage of walrus operators.

cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit