[SPARK-17793][WEB UI] Sorting on the description on the Job or Stage page doesn’t always work

## What changes were proposed in this pull request?

Added secondary sorting on stage name for the description column. This provide a clearer behavior in the common case where the Description column only comprises of Stage names instead of the option description value.

## How was this patch tested?

manual testing and dev/run-tests

Screenshots of sorting on both description and stage name as well as an example of both:
![screen shot 2016-10-04 at 1 09 39 pm](https://cloud.githubusercontent.com/assets/13952758/19135523/067b042e-8b1a-11e6-912e-e6371d006d21.png)
![screen shot 2016-10-04 at 1 09 51 pm](https://cloud.githubusercontent.com/assets/13952758/19135526/06960936-8b1a-11e6-85e9-8aaf694c5f7b.png)
![screen shot 2016-10-05 at 1 14 45 pm](https://cloud.githubusercontent.com/assets/13952758/19135525/069547da-8b1a-11e6-8692-6524c75c4c07.png)
![screen shot 2016-10-05 at 1 14 51 pm](https://cloud.githubusercontent.com/assets/13952758/19135524/0694b4d2-8b1a-11e6-92dc-c8aa514e4f62.png)
![screen shot 2016-10-05 at 4 42 52 pm](https://cloud.githubusercontent.com/assets/13952758/19135618/e232eafe-8b1a-11e6-88b3-ff0bbb26b7f8.png)

Author: Alex Bozarth <ajbozart@us.ibm.com>

Closes #15366 from ajbozarth/spark17793.