[SPARK-7664] [WEBUI] DAG visualization: Fix incorrect link paths of DAG.

In JobPage, we can jump a StagePage when we click corresponding box of DAG viz but the link path is incorrect.

When we click a box like as follows ...
![screenshot_from_2015-05-15 19 24 25](https://cloud.githubusercontent.com/assets/4736016/7651528/5f7ef824-fb3c-11e4-9518-8c9ade2dff7a.png)

We jump to index page.
![screenshot_from_2015-05-15 19 24 45](https://cloud.githubusercontent.com/assets/4736016/7651534/6d666274-fb3c-11e4-971c-c3f2dc2b1da2.png)

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #6184 from sarutak/fix-link-path-of-dag-viz and squashes the following commits:

faba3ba [Kousuke Saruta] Fix a incorrect link

core/src/main/resources/org/apache/spark/ui/static/spark-dag-viz.js

@@ -186,8 +186,9 @@ function renderDagVizForJob(svgContainer) {
     var stageId = metadata.attr("stage-id");
     var containerId = VizConstants.graphPrefix + stageId;
     // Link each graph to the corresponding stage page (TODO: handle stage attempts)
-    var stageLink = "/stages/stage/?id=" +
-      stageId.replace(VizConstants.stagePrefix, "") + "&attempt=0&expandDagViz=true";
+    var stageLink = $("#stage-" + stageId.replace(VizConstants.stagePrefix, "") + "-0")
+      .find("a")
+      .attr("href") + "&expandDagViz=true";
     var container = svgContainer
       .append("a")
       .attr("xlink:href", stageLink)