Returns the container id when running in a Docker container.
This inspects /proc/self/cgroup looking for a Kubernetes Control Group. Once it finds one it attempts
to isolate just the docker container id. There doesn't appear to be a standard way to do this, but
it seems to be the only way to determine what the current container is in a multi-container pod. It would have
been much nicer if Kubernetes would just put the container id in a standard environment variable.
See Also:
Stackoverflow for a discussion on retrieving the containerId.,