Enable backoff/retries on scaling up

- this change is needed for Docker Swarm which may give an error
when several concurrent requests come in to scale a deployment.

Tested on Docker Swarm before/after with the hey tool and figlet
scaled down to zero replicas.

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

gateway/server.go

@@ -137,7 +137,8 @@ func main() {
 	if config.ScaleFromZero {
 		scalingConfig := scaling.ScalingConfig{
 			MaxPollCount:         uint(1000),
-			FunctionPollInterval: time.Millisecond * 10,
+			SetScaleRetries:      uint(20),
+			FunctionPollInterval: time.Millisecond * 50,
 			CacheExpiry:          time.Second * 5, // freshness of replica values before going stale
 			ServiceQuery:         alertHandler,
 		}