Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Improve codes which checks whether sandbox contains containers
Currently evictSandboxes() checks whether sandbox contains
containers, it traverses all the containers for every sandbox,
but when cluster has many containres, it wastes a lot of time.
It is better to use sets in this case.
**Release note**:
```release-note
NONE
```