[SPARK-20591][WEB UI] Succeeded tasks num not equal in all jobs page and job detail page on spark web ui when speculative task(s) exist.

## What changes were proposed in this pull request?

Modified succeeded num in job detail page from "completed = stageData.completedIndices.size" to "completed = stageData.numCompleteTasks",which making succeeded tasks num in all jobs page and job detail page look more consistent, and more easily to find which stages the speculative task(s) were in.

## How was this patch tested?

manual tests

Author: fjh100456

core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala

@@ -299,7 +299,7 @@ private[ui] class StagePagedTable(
         <td>{data.formattedDuration}</td>
         <td class="progress-cell">
           {UIUtils.makeProgressBar(started = stageData.numActiveTasks,
-          completed = stageData.completedIndices.size, failed = stageData.numFailedTasks,
+          completed = stageData.numCompleteTasks, failed = stageData.numFailedTasks,
           skipped = 0, reasonToNumKilled = stageData.reasonToNumKilled, total = info.numTasks)}
         </td>
         <td>{data.inputReadWithUnit}</td>