[SPARK-14702] Make environment of SparkLauncher launched process more configurable

## What changes were proposed in this pull request?

Adds a few public methods to `SparkLauncher` to allow configuring some extra features of the `ProcessBuilder`, including the working directory, output and error stream redirection.

## How was this patch tested?

Unit testing + simple Spark driver programs

Author: Andrew Duffy <root@aduffy.org>

Closes #14201 from andreweduffy/feature/launcher.