tool/exchange_wrapper_coverage: fix regression and implement reflection (#837)

* cmd/tools/exchange: fix regression and implement reflection so as this can dynamically scale to our interface

* exchanges: add comment and fix whoopsie

* exchanges: fix linter issues

* wrapper_cov_tool: add actual full interface method count to get a better perceived deployment

* exchanges/tool: addr glorious nits

* kraken: remove string in test

* exchange_template_tool: fix tmpl issue

engine/engine.go

@@ -861,13 +861,15 @@ func (bot *Engine) LoadExchange(name string, wg *sync.WaitGroup) error {
 	}
 
 	if wg != nil {
-		exch.Start(wg)
-	} else {
-		tempWG := sync.WaitGroup{}
-		exch.Start(&tempWG)
-		tempWG.Wait()
+		return exch.Start(wg)
 	}
 
+	tempWG := sync.WaitGroup{}
+	err = exch.Start(&tempWG)
+	if err != nil {
+		return err
+	}
+	tempWG.Wait()
 	return nil
 }