Support http service graceful restart (#416)

* support http service graceful restart

* fix dependencies

vendor/github.com/facebookgo/stats/aggregation.go

@@ -0,0 +1,35 @@
+package stats
+
+import "sort"
+
+// Average returns the average value
+func Average(values []float64) float64 {
+	if len(values) == 0 {
+		return 0
+	}
+
+	var val float64
+	for _, point := range values {
+		val += point
+	}
+	return val / float64(len(values))
+}
+
+// Sum returns the sum of all the given values
+func Sum(values []float64) float64 {
+	var val float64
+	for _, point := range values {
+		val += point
+	}
+	return val
+}
+
+// Percentiles returns a map containing the asked for percentiles
+func Percentiles(values []float64, percentiles map[string]float64) map[string]float64 {
+	sort.Float64s(values)
+	results := map[string]float64{}
+	for label, p := range percentiles {
+		results[label] = values[int(float64(len(values))*p)]
+	}
+	return results
+}