[SPARK-16673][WEB UI] New Executor Page removed conditional for Logs and Thread Dump columns

## What changes were proposed in this pull request?

When #13670 switched `ExecutorsPage` to use JQuery DataTables it incidentally removed the conditional for the Logs and Thread Dump columns. I reimplemented the conditional display of the Logs and Thread dump columns as it was before the switch.

## How was this patch tested?

Manually tested and dev/run-tests

![both](https://cloud.githubusercontent.com/assets/13952758/17186879/da8dd1a8-53eb-11e6-8b0c-d0ff0156a9a7.png)
![dump](https://cloud.githubusercontent.com/assets/13952758/17186881/dab08a04-53eb-11e6-8b1c-50ffd0bf2ae8.png)
![logs](https://cloud.githubusercontent.com/assets/13952758/17186880/dab04d00-53eb-11e6-8754-68dd64d6d9f4.png)

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

Closes #14382 from ajbozarth/spark16673.