vendor: initial vendor

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

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

@@ -0,0 +1,10 @@
+package metrics
+
+func sumFloat64(vs ...float64) float64 {
+	var sum float64
+	for _, v := range vs {
+		sum += v
+	}
+
+	return sum
+}