Add UTCNow() function. (#3931)

This patch adds UTCNow() function which returns current UTC time.

This is equivalent of UTCNow() == time.Now().UTC()

cmd/retry.go

@@ -54,7 +54,7 @@ const NoJitter = 0.0
 
 // Global random source for fetching random values.
 var globalRandomSource = rand.New(&lockedRandSource{
-	src: rand.NewSource(time.Now().UTC().UnixNano()),
+	src: rand.NewSource(UTCNow().UnixNano()),
 })
 
 // newRetryTimerJitter creates a timer with exponentially increasing delays