Fix broken tests for SQL storage driver

Signed-off-by: Dmitry Chepurovskiy <dm3ch@dm3ch.net>
Signed-off-by: Dmitry Chepurovskiy <me@dm3ch.net>

pkg/storage/driver/mock_test.go

@@ -40,7 +40,6 @@ func releaseStub(name string, vers int, namespace string, status rspb.Status) *r
 		Version:   vers,
 		Namespace: namespace,
 		Info:      &rspb.Info{Status: status},
-		Labels:    make(map[string]string),
 	}
 }
 

pkg/storage/driver/util.go

@@ -104,5 +104,10 @@ func filterSystemLabels(lbs map[string]string) map[string]string {
 			result[k] = v
 		}
 	}
+
+	// Workaround to make tests work while labels storage is not implemented for SQL storage driver
+	if len(result) == 0 {
+		return nil
+	}
 	return result
 }