setExecutorCount doesn't allow set group count to 0, so spark job can't stop naturally

[tantra35]

In last changes setExecutorCount was changed as:

  def setExecutorCount(count: Int): Unit = {
    jobManipulator.updateJob(startIfNotYetRunning = count > 0) { job =>
      val executorGroup = SparkNomadJob.find(job, ExecutorTaskGroup).get
      if (count > 0 && executorGroup.getCount < count) {
        executorGroup.setCount(count)
      }
    }
  }

but this is wrong because, no any chance to set nomad task group count to 0(this used to stop spark job), and right changes should be as follow

  def setExecutorCount(count: Int): Unit = {
    jobManipulator.updateJob(startIfNotYetRunning = count > 0) { job =>
      val executorGroup = SparkNomadJob.find(job, ExecutorTaskGroup).get
      if (count > 0 && executorGroup.getCount < count) {
        executorGroup.setCount(count)
      } else if (count == 0) {
        executorGroup.setCount(0)
      }
    }
  }