code: public void kill(TaskID taskId) {
      Builder kill = build().setKill(Kill.newBuilder().setTaskId(taskId));
      sendCall(kill, Type.KILL);
    }
docs: Sent by the scheduler to kill a specific task. If the scheduler has a custom executor, the kill is
  forwarded to the executor; it is up to the executor to kill the task and send a TASK_KILLED
  (or TASK_FAILED) update. If the task hasn’t yet been delivered to the executor when Mesos master or
  agent receives the kill request, a TASK_KILLED is generated and the task launch is not forwarded to
  the executor. Note that if the task belongs to a task group, killing of one task results in all tasks
  in the task group being killed. Mesos releases the resources for a task once it receives a terminal
  update for the task. If the task is unknown to the master, a TASK_LOST will be generated.
  
  @param taskId