## What changes were proposed in this pull request?

- enable setting default properties for all jobs submitted through the dispatcher [SPARK-16927]
- remove duplication of conf vars on cluster submitted jobs [SPARK-16923] (this is a small fix, so I'm including in the same PR)

## How was this patch tested?

mesos/spark integration test suite
manual testing

Author: Timothy Chen <tnachen@gmail.com>

Closes #14511 from mgummelt/override-props.