[caffe2] add PlanExecutorTest ErrorPlanWithCancellableStuckNet (#46110)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46110
## Motivation
* `Cancel` is now added to `OperatorBase` and `NetBase` (https://github.com/pytorch/pytorch/pull/44145).
* We need a test to cover and exhibit that we can cancel stuck net and propagate error with plan executor.
## Summary
* Added PlanExecutorTest `ErrorPlanWithCancellableStuckNet` for plan executor.
* Set cancelCount to zero at the beginning of tests to avoid global state be carried over in some test environment.
Test Plan:
## Unit Test Added
```
buck test caffe2/caffe2:caffe2_test_cpu -- PlanExecutorTest
buck test caffe2/caffe2:caffe2_test_cpu -- PlanExecutorTest --stress-runs 1000
```
Reviewed By: d4l3k
Differential Revision: D24226577
fbshipit-source-id: c834383bfe6ab50747975c229eb42a363eed3458
