Issue #699 Return codes for prom server

src/apps/relay/mainrelay.c

@@ -2589,9 +2589,13 @@ int main(int argc, char **argv)
 
 	drop_privileges();
 #if !defined(TURN_NO_PROMETHEUS)
-	if (start_prometheus_server()){
+	int prometheus_status = start_prometheus_server();
+	if (prometheus_status < 0) {
 	  TURN_LOG_FUNC(TURN_LOG_LEVEL_ERROR, "Could not start Prometheus collector!\n");
 	}
+	else if (prometheus_status == 1) {
+	  TURN_LOG_FUNC(TURN_LOG_LEVEL_INFO, "Prometheus collector disabled, not started.\n");
+	}
 	else {
 	  TURN_LOG_FUNC(TURN_LOG_LEVEL_INFO, "Prometheus collector started successfully.\n");
 	}

src/apps/relay/prom_server.c

@@ -62,7 +62,7 @@ int start_prometheus_server(void){
 
   struct MHD_Daemon *daemon = promhttp_start_daemon(MHD_USE_SELECT_INTERNALLY, DEFAULT_PROM_SERVER_PORT, NULL, NULL);
   if (daemon == NULL) {
-    return 1;
+    return -1;
   }
   return 0;
 }