Automatic merge from submit-queue (batch tested with PRs 66351, 66883, 66156). 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>.

Add unit tests to cover scopes and scope selectors during quota sync logic

**What this PR does / why we need it**:
Adds unit tests to cover scopes and scope selectors fields in the quota spec. Existing unit test for quota sync does not cover scopes.

Also while adding tests found a minor issue with 'Exists' scope selector operator. This is also being fixed in this PR.

**Special notes for your reviewer**:

**Release note**:

```release-note
Unit tests for scopes and scope selectors in the quota spec
```
/cc @derekwaynecarr @sjenning @bsalamat @kubernetes/sig-scheduling-pr-reviews @kubernetes/sig-node-pr-reviews