[DEPLOY] SPARK-3759: Return the exit code of the driver process

SparkSubmitDriverBootstrapper.scala now returns the exit code of the driver process, instead of always returning 0.

Author: Eric Eijkelenboom <ee@userreport.com>

Closes #2628 from ericeijkelenboom/master and squashes the following commits:

cc4a571 [Eric Eijkelenboom] Return the exit code of the driver process