Libcontainer fs.GetStats() will not look for cgroups relative to the cgroup of init process if the parent
in cgroups.Cgroup is absolute. This is required to get stats of other containers while running inside a docker container.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Merge pull request #130 from vishh/fix_cgroup_path

Make fs.GetStats() work when used from inside a docker container.