Scala 2.12 Cleanup Tasks (No Milestone)

[KenSuenobu]

Here's a list of some cleanups that should be done when shifting to Scala 2.12.x branch after Spark is converted to Scala 2.12. No milestone is set for this, as this timeline is uncertain.

[KenSuenobu]

ShellTask:

  if (process.isAlive()) {
    logger.info("Process is still running; terminating.")
    process.destroy()
  }

[KenSuenobu]

Spark 2.4.0 release is coming soon. Once the 2.4.x branch is released, it will be a good time to switch to Spark 2.12.x. Should be noted that the current ticket to close Scala 2.12.x functionality with Spark has been closed, which means it now compiled in Scala 2.12.