Automatic merge from submit-queue (batch tested with PRs 46383, 45645, 45923, 44884, 46294)

Created unit tests for GCE cloud provider storage interface.

- Currently covers CreateDisk and DeleteDisk, GetAutoLabelsForPD
- Created ServiceManager interface in gce.go to facilitate mocking in tests.



**What this PR does / why we need it**:
Increasing test coverage for GCE Persistent Disk.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #44573 

**Release note**:

```release-note
NONE
```