Add VolumeSnapshotBeingDeleted annotation to content

[xing-yang]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR adds VolumeSnapshotBeingDeleted annotation to the VolumeSnapshotContent object before the finalizers on the VolumeSnapshot object is removed. This is to make sure that the annotation is on the Content before VolumeSnapshot object is removed from the API server.

Which issue(s) this PR fixes:
Fixes #248

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Fixes a problem deleting VolumeSnapshotContent with `Retain` policy for pre-provisioned snapshots.

[xing-yang]

/assign @yuxiangqian

[xing-yang]

@yuxiangqian can you review this?

[yuxiangqian]

LGTM, can you add a test case?

[jsafrane]

I got lost in snapshot finalizers... With this PR, snapshot-controller adds annotation and exernal-snapshotter, seeing the annotation, removes the finalizer. Can the snapshot-controller remove the finalizer right away?

[xing-yang]

I got lost in snapshot finalizers... With this PR, snapshot-controller adds annotation and exernal-snapshotter, seeing the annotation, removes the finalizer. Can the snapshot-controller remove the finalizer right away?

This is to avoid leaking of the physical snapshot on the storage system. We want to make sure the physical snapshot is deleted from the storage system before removing the finalizer if the deletion policy is Delete. It is possible to remove finalizer from the content in the snapshot-controller if the policy is Retain, but we'd like to keep the content finalizer removal logic in one place which is the sidecar external-snapshotter.

[jsafrane]

Ack

[xing-yang]

@yuxiangqian Unit test added. PTAL.

[yuxiangqian]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xing-yang, yuxiangqian

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[leshibily]

@xing-yang how did I add the annotation? or snapshot-controller adds the annotation, what config should I do to make it happen?

[xing-yang]

@leshibily This annotation is added internally by the snapshot-controller. You should not be adding it manually. Also it will be removed by the snapshot-controller after the snapshot is deleted from the storage system.

[DSO-TB]

@xing-yang I am currently running on 6.0.1 and still facing issues with volumesnapshotcontents not being deleted. I have verified that the code from the commit is there and when I remove the finalizer they delete fine. Anything I can check in the annotations to verify that everything is correct or is there another issue open I can reference?

[xing-yang]

@DSO-TB Can you open an issue, describe your testing steps and provide logs?