Add prometheus container level metrics

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/containerd/builtins.go

@@ -3,6 +3,7 @@ package main
 // register containerd builtins here
 import (
 	_ "github.com/docker/containerd/linux"
+	_ "github.com/docker/containerd/metrics/cgroups"
 	_ "github.com/docker/containerd/services/content"
 	_ "github.com/docker/containerd/services/execution"
 	_ "github.com/docker/containerd/services/healthcheck"