Delay removing of task if dependent tasks are still running

[soichih]

When I have a task A followed by B where A is finished but B is currently running, stop_requested on task A should delay fulfilling the request until B is finished, removed, or failed.

Related to this..

Let's say task A is submitted, and 25 days later task B is submitted. By the time B gets executed, A may already be removed and task B will fail (or currently, it seems to get stuck waiting on dependencies A that are forever stuck in "removed" state).

If B is waiting on A and A's task is removed, I believe I should resubmit A (which then cascade to run A's parent, and so on).

• This case also happens if user tries to rerun Task B after A is removed.

If task B gets executed and realizes that task A is failed, this case is already handled by the task handler by failing the task B immediately.