fix: capture Run() error in metrics controller goroutine

The goroutine was referencing the outer 'err' variable from
metrics.NewController() instead of capturing the return value
from metricsController.Run(). By the time the goroutine executes,
the outer err is nil (NewController succeeded), so the log line
always printed a nil error — making failures impossible to diagnose.

Fixes #325

Author: abhaygoudannavar

main.go

@@ -287,10 +287,14 @@ func main() {
 	externalScaler := externalscaler.NewExternalScaler(mgr.GetClient())
 	go func() {
 		grpcServer := grpc.NewServer()
-		lis, _ := net.Listen("tcp", scaleServerAddr)
+		lis, err := net.Listen("tcp", scaleServerAddr)
+		if err != nil {
+			setupLog.Error(err, "unable to listen for ExternalScalerServer", "address", scaleServerAddr)
+			os.Exit(1)
+		}
 		externalscaler.RegisterExternalScalerServer(grpcServer, externalScaler)
 		if err := grpcServer.Serve(lis); err != nil {
-			setupLog.Error(err, "unable to setup ExternalScalerServer")
+			setupLog.Error(err, "unable to serve ExternalScalerServer")
 			os.Exit(1)
 		}
 	}()