Fix PVC ModifyVolume conditions

[AndrewSirenko]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

/kind bug

What this PR does / why we need it:

Ensures PVCs associated with failed volume modifications always have both pvcModifyingVolumeCondition and pvcModifyVolumeErrorCondition

Also refactors pkg/modify_volume.go to have clearer flow and less duplicate logic.

Draft NOTE: PR stacked on top of to prevent merge conflicts. Will need to rebase against merged PR before undrafting.

Which issue(s) this PR fixes:

Fixes #483

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Ensure PVCs associated with failed volume modifications have correct conditions

[k8s-ci-robot]

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: AndrewSirenko
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[k8s-ci-robot]

PR needs rebase.

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