Add prometheus container level metrics

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

vendor/github.com/crosbymichael/cgroups/named.go

@@ -0,0 +1,23 @@
+package cgroups
+
+import "path/filepath"
+
+func NewNamed(root string, name Name) *namedController {
+	return &namedController{
+		root: root,
+		name: name,
+	}
+}
+
+type namedController struct {
+	root string
+	name Name
+}
+
+func (n *namedController) Name() Name {
+	return n.name
+}
+
+func (n *namedController) Path(path string) string {
+	return filepath.Join(n.root, string(n.name), path)
+}