### What changes were proposed in this pull request?
This PR modifies the POD allocator to use the scheduler backend to get the known executors and remove those from the pending and newly created list.
This is different from the normal `ExecutorAllocationManager` requested killing of executors where the `spark.dynamicAllocation.executorIdleTimeout` is used.
In this case POD allocator kills the executors which should be only responsible for terminating not satisfied POD allocations (new requests where no POD state is received yet and PODs in pending state).
### Why are the changes needed?
Because there is race between executor POD allocator and cluster scheduler backend.
Running several experiment during downscaling we experienced a lot of killed fresh executors wich has already running task on them.
The pattern in the log was the following (see executor 312 and TID 2079):
```
21/02/01 15:12:03 INFO ExecutorMonitor: New executor 312 has registered (new total is 138)
...
21/02/01 15:12:03 INFO TaskSetManager: Starting task 247.0 in stage 4.0 (TID 2079, 100.100.18.138, executor 312, partition 247, PROCESS_LOCAL, 8777 bytes)
21/02/01 15:12:03 INFO ExecutorPodsAllocator: Deleting 3 excess pod requests (408,312,307).
...
21/02/01 15:12:04 ERROR TaskSchedulerImpl: Lost executor 312 on 100.100.18.138: The executor with id 312 was deleted by a user or the framework.
21/02/01 15:12:04 INFO TaskSetManager: Task 2079 failed because while it was being computed, its executor exited for a reason unrelated to the task. Not counting this failure towards the maximum number of failures for the task.
```
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
#### Manually
With this change there was no executor lost with running task on it.
##### With unit test
A new test is added and existing test is modified to check these cases.
Closes#31513 from attilapiros/SPARK-34361.
Authored-by: “attilapiros” <piros.attila.zsolt@gmail.com>
Signed-off-by: Holden Karau <hkarau@apple.com>
6c5322de61