Automatic merge from submit-queue (batch tested with PRs 52831, 52764, 52763, 52673, 52558). 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>..

Minor fix: make sure that glusterfsPlugin implements interface ExpandableVolumePlugin

Attempting an assignment to make sure that `glusterfsPlugin`  implements interface `ExpandableVolumePlugin`, just as we did for `DeletableVolumePlugin`, `PersistentVolumePlugin`


**What this PR does / why we need it**:

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

**Special notes for your reviewer**:

**Release note**:
```release-note
NONE
```

/assign @gnufied