stats: fix stats when systemd cgroups are used
stats: fix stats when systemd cgroups are used

passing the slice directly to libpod.cgroups.Load() caused it to not be found. This is because it expected a fully qualified path, rather than a slice name.
write a function to translate slice name to path, and pass that down if we're using systemd cgroups

Signed-off-by: Peter Hunt <fb7b1ad57b81f1e149129d77ecccc59c02fe0648@redhat.com>

kubernetes-incubator/ocid,mikebrow/cri-o,kubernetes-incubator/cri-o,mikebrow/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/ocid,kubernetes-incubator/cri-o,kubernetes-incubator/cri-o,nalind/cri-o,nalind/cri-o,mikebrow/cri-o,mikebrow/cri-o,nalind/cri-o,kubernetes-incubator/cri-o