Another fix for a flaky Selenium test.
Another fix for a flaky Selenium test.

edx-solutions/xblock-drag-and-drop-v2,open-craft/xblock-drag-and-drop-v2,arbrandes/xblock-drag-and-drop-v2,edx-solutions/xblock-drag-and-drop-v2,arbrandes/xblock-drag-and-drop-v2,edx-solutions/xblock-drag-and-drop-v2,arbrandes/xblock-drag-and-drop-v2,edx-solutions/xblock-drag-and-drop-v2,open-craft/xblock-drag-and-drop-v2,open-craft/xblock-drag-and-drop-v2,arbrandes/xblock-drag-and-drop-v2,open-craft/xblock-drag-and-drop-v2