Add prometheus container level metrics

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

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

@@ -0,0 +1,21 @@
+package cgroups
+
+import "path/filepath"
+
+func NewPerfEvent(root string) *PerfEventController {
+	return &PerfEventController{
+		root: filepath.Join(root, string(PerfEvent)),
+	}
+}
+
+type PerfEventController struct {
+	root string
+}
+
+func (p *PerfEventController) Name() Name {
+	return PerfEvent
+}
+
+func (p *PerfEventController) Path(path string) string {
+	return filepath.Join(p.root, path)
+}