Refactor agent (#2021)

- code cleanup
- init backend engine only once
- pass a taskUUID to the backend

---
*Sponsored by Kithara Software GmbH*

cmd/agent/agent.go

@@ -215,20 +215,20 @@ func run(c *cli.Context) error {
 		}
 	}()
 
+	// load engine (e.g. init api client)
+	if err := engine.Load(backendCtx); err != nil {
+		log.Error().Err(err).Msg("cannot load backend engine")
+		return err
+	}
+	log.Debug().Msgf("loaded %s backend engine", engine.Name())
+
 	for i := 0; i < parallel; i++ {
+		i := i
 		go func() {
 			defer wg.Done()
 
-			// load engine (e.g. init api client)
-			err = engine.Load(backendCtx)
-			if err != nil {
-				log.Error().Err(err).Msg("cannot load backend engine")
-				return
-			}
-
 			r := agent.NewRunner(client, filter, hostname, counter, &engine)
-
-			log.Debug().Msgf("loaded %s backend engine", engine.Name())
+			log.Debug().Msgf("created new runner %d", i)
 
 			for {
 				if sigterm.IsSet() {