Improve implementation of QueryTaskExecuter

Current implementation is based on StrippedThreadExecutor which has major downside: long-living task prevents others task from the same stripe from being executed. This means that the sql engine can be blocked by any query that will take a thread for a long time (most simple example is UDF invoking a Thread.sleep()).

Let's think about how we can improve this.

Every implementation of QueryTaskExecuter must meet following requirements:

1. tasks with the same (queryId, fragmentId) can't be reordered
2. tasks with the same (queryId, fragmentId) can't be executed in parallel: if T1 and T2 are tasks, submit_time(T1) < submit_time(T2), then end_time(T1) < start_time(T2)
3. there must be 'happens-before' relation between execution of task with the same (queryId, fragmentId)