…storage_test

juju#14625

Covered by new bash based tests.

## Checklist

*If an item is not applicable, use `~strikethrough~`.*

- ~[ ] Code style: imports ordered, good names, simple structure, etc~
- ~[ ] Comments saying why design decisions were made~
- ~[ ] Go unit tests, with comments saying what you're testing~
- ~[ ] [Integration tests](https://github.com/juju/juju/tree/develop/tests), with comments saying what you're testing~
- ~[ ] [doc.go](https://discourse.charmhub.io/t/readme-in-packages/451) added or updated in changed packages~