This implements cgroup.Apply() using the systemd apis.
We create a transient unit called "docker-$id.scope" that contains
the container processes. We also have a way to set unit specific
properties, currently only defining the Slice to put the
scope in.
Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
