udisks2: Handle NotAuthorizedCanObtain and NotAuthorizedDismissed
Otherwise we'd show "an unspecified error has occurred".
- NotAuthorizedCanObtain means that e.g. no polkit agent is running and thus it didn't authorize but it otherwise likely could have.
- NotAuthorizedDismissed means the user cancelled the auth prompt. Ideally, we treated this as "cancelled" without raising an error.