mysql: minor progress on response processing

pkg/api/metrics.go

@@ -50,6 +50,12 @@ func QueryMetrics(c *middleware.Context, reqDto dtos.MetricRequest) Response {
 		return ApiError(500, "Metric request error", err)
 	}
 
+	for _, res := range resp.Results {
+		if res.Error != nil {
+			res.ErrorString = res.Error.Error()
+		}
+	}
+
 	return Json(200, &resp)
 }