Retrieve the VolumeSnapshotContent before attempting an update

[huffmanca]

What type of PR is this?
/kind bug

What this PR does / why we need it:
It's been noticed that when we attempt to update the VSC's error the following error can be thrown:

I0525 13:07:49.293034       1 snapshot_controller.go:165] updating VolumeSnapshotContent[snapcontent-f24fd046-1664-4bb2-bb43-f91ae0909b02] error status failed Operation cannot be fulfilled on volumesnapshotcontents.snapshot.storage.k8s.io "snapcontent-f24fd046-1664-4bb2-bb43-f91ae0909b02": the object has been modified; please apply your changes to the latest version and try again

This PR forces a Get before we attempt the update so that we can avoid this error.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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[ggriffiths]

These seems to cut the number of errors in half from 56 to 28:

with this change:

~ curl -s https://storage.googleapis.com/kubernetes-jenkins/pr-logs/pull/kubernetes-csi_external-snapshotter/524/pull-kubernetes-csi-external-snapshotter-1-21-on-kubernetes-1-21/1397246208530976768/artifacts/kube-system/snapshot-controller-58f54d8f6c-7t6tx/snapshot-controller.log | grep 'the object has been modified; please apply your' | wc -l
      28

without:

~ curl -s https://storage.googleapis.com/kubernetes-jenkins/pr-logs/pull/kubernetes-csi_external-snapshotter/519/pull-kubernetes-csi-external-snapshotter-1-21-on-kubernetes-1-21/1396873247164731392/artifacts/kube-system/snapshot-controller-58f54d8f6c-9gt8c/snapshot-controller.log |  grep 'the object has been modified; please apply your' | wc -l
      56

I believe there was a concern about excessive API calls if we get the latest object before every update, but this will only pull the latest object for updateContentErrorStatusWithEvent. I think it's okay to add this change as a temporary improvement until a permanent fix is added. Thoughts on this @xing-yang ?

[xing-yang]

I believe there was a concern about excessive API calls if we get the latest object before every update, but this will only pull the latest object for updateContentErrorStatusWithEvent. I think it's okay to add this change as a temporary improvement until a permanent fix is added. Thoughts on this @xing-yang ?

I still have this concern. Let's discuss about this in the CSI meeting.

[huffmanca]

I was watching #480 to see if it would get merged, but after it was closed I submitted this PR in the hopes of addressing one of the issues. Right now we can encounter a state where an error isn't added to the VSC due to constant object has been modified errors.

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@huffmanca: PR needs rebase.

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