Opt into KIO changes for cgroup management
Summary:
It was safeguarded by an environment variable so we don't retroactively
change behaviour of existing setups in a bugfix update.
See https://phabricator.kde.org/D27883
Test Plan: Compiles
Reviewers: Plasma, apol
Reviewed By: apol
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D28300