Exit cleanly when max-sigterm-delay is enabled

When the client closes cleanly and max-sigterm-delay is enabled, the
Proxy will exit with a 0 exit code on SIGTERM or SIGINT.

Otherwise, the Proxy will exit with 143 (SIGTERM) or 130 (SIGINT).

cmd/root.go

@@ -617,11 +617,6 @@ func runSignalWrapper(cmd *Command) error {
 	case p = <-startCh:
 		cmd.logger.Infof("The proxy has started successfully and is ready for new connections!")
 	}
-	defer func() {
-		if cErr := p.Close(); cErr != nil {
-			cmd.logger.Errorf("error during shutdown: %v", cErr)
-		}
-	}()
 
 	notify := func() {}
 	if cmd.healthCheck {
@@ -672,5 +667,14 @@ func runSignalWrapper(cmd *Command) error {
 	default:
 		cmd.logger.Errorf("The proxy has encountered a terminal error: %v", err)
 	}
+	cErr := p.Close()
+	if cErr != nil {
+		cmd.logger.Errorf("error during shutdown: %v", cErr)
+	}
+	// If Close succeeded and WaitOnClose is enabled, return no error to get a 0
+	// exit status.
+	if cErr == nil && cmd.conf.WaitOnClose != 0 {
+		return nil
+	}
 	return err
 }