Comment 4 for bug 1534627

Dead models are kept around in the DB for post-mortems. There's a couple of issues with this:
 - dead models still show up in list-models
 - you can "juju switch" to dead models
 - dead models can be referenced by commands (e.g. "juju destroy-model" will happily destroy a previously destroyed model, provided you switch to them first)
 - the names of dead models cannot be reused until the model is eventually reaped from the DB

I think we should look at renaming models when they're set to "dead", such that the name can be reused; and we should not allow dead models to leak into the UI, except perhaps when explicitly requested.