Comment 8 for bug 1946382

The life permission warning turns out to be bogus - the provisioner worker was not properly accounting for the fact that storage attachments go from dying->removed. This PR fixes that plus an issue observed along the way, whereby storage attachment was meant to be idempotent but there was a logic error that caused a silly error to be printed when using the CLI.

https://github.com/juju/juju/pull/13516