Update containerd to 129167132c.

Signed-off-by: Lantao Liu <lantaol@google.com>

vendor/github.com/docker/go-metrics/handler.go

@@ -0,0 +1,13 @@
+package metrics
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Handler returns the global http.Handler that provides the prometheus
+// metrics format on GET requests
+func Handler() http.Handler {
+	return prometheus.Handler()
+}