https://issues.apache.org/jira/browse/SPARK-17724

## What changes were proposed in this pull request?
For unevaluated `\n`, evaluate it and enable line break, for Streaming WebUI `stages` page and `job` page.
(I didn't change Scala source file, since Jetty server has to somehow indicate line break and js to code display it.)
(This PR is a continue from previous PR https://github.com/apache/spark/pull/15353 for the same issue, sorry being so long time)

Two changes:

1. RDD Node tooltipText is actually showing the `<circle>`  `title` property, so I set extra attribute in `spark-dag-viz.js`: `.attr("data-html", "true")`

`<circle x="-5" y="-5" r="5" data-toggle="tooltip" data-placement="bottom" title="" data-original-title="ParallelCollectionRDD [9]\nmakeRDD at QueueStream.scala:49"></circle>`

2. Static `<tspan>` text of each stage, split by `/n`, and append an extra `<tspan>` element to its parentNode

`<text><tspan xml:space="preserve" dy="1em" x="1">reduceByKey</tspan><tspan xml:space="preserve" dy="1em" x="1">reduceByKey/n 23:34:49</tspan></text>
`

## UI changes
Screenshot **before fix**, `\n` is not evaluated in both circle tooltipText and static text:
![screen shot 2017-01-19 at 12 21 54 am](https://cloud.githubusercontent.com/assets/3925641/22098829/53c7f49c-dddd-11e6-9daa-b3ddb6044114.png)

Screenshot **after fix**:
![screen shot 2017-01-19 at 12 20 30 am](https://cloud.githubusercontent.com/assets/3925641/22098806/294910d4-dddd-11e6-9948-d942e09f545e.png)

## How was this patch tested?
Tested locally. For Streaming WebUI `stages` page and `job` page, on multiple browsers:
- Chrome
- Firefox
- Safari

Author: Xin Ren <renxin.ubc@gmail.com>

Closes #16643 from keypointt/SPARK-17724-2nd.