Add baselines, mark flaky test

Author: dy

test/image/baselines/gl2d_scatter-color-clustering.png

@@ -64,7 +64,7 @@ var mock4 = {
     layout: {}
 };
 
-describe('@gl Test hover and click interactions', function() {
+describe('@gl @flaky Test hover and click interactions', function() {
     var gd;
 
     function makeHoverFn(gd, x, y) {