Make container runtime's cgroup configurable.

Use the real cgroups for metrics generation.

Signed-off-by: Vishnu kannan <vishnuk@google.com>

docs/admin/kubelet.md

@@ -139,6 +139,7 @@ kubelet
       --rkt-stage1-image="": image to use as stage1. Local paths and http/https URLs are supported. If empty, the 'stage1.aci' in the same directory as '--rkt-path' will be used
       --root-dir="/var/lib/kubelet": Directory path for managing kubelet files (volume mounts,etc).
       --runonce[=false]: If true, exit after spawning pods from local manifests or remote urls. Exclusive with --api-servers, and --enable-server
+      --runtime-container="/docker-daemon": Absolute name of the cgroups to create (if required) and run the runtime in (Default: /docker-daemon).
       --serialize-image-pulls[=true]: Pull images one at a time. We recommend *not* changing the default value on nodes that run docker daemon with version < 1.9 or an Aufs storage backend. Issue #10959 has more details. [default=true]
       --streaming-connection-idle-timeout=4h0m0s: Maximum time a streaming connection can be idle before the connection is automatically closed. 0 indicates no timeout. Example: '5m'
       --sync-frequency=1m0s: Max period between synchronizing running containers and config