juju allows deploying charms with protected interfaces

[Pietro Pasotti]

Juju allows you to deploy a charm declaring 'protected' interfaces such as `juju-info` and `juju-dashboard`, only to later fail when doing `juju run`.

Interestingly enough the charm seems to work well for the rest, only when trying to run an action, things break.
The charm goes then into 'active/failed` status and the logs show:

```
unit-facade1-0: 12:14:17 ERROR juju.worker.uniter resolver loop error: preparing operation "run action 29" for facade1/0: cannot crea
te runner for action "29": charm "facade" relation "provide-juju-dashboard" using a reserved interface: "juju-dashboard"
unit-facade1-0: 12:14:17 INFO juju.worker.uniter unit "facade1/0" shutting down: preparing operation "run action 29" for facade1/0: c
annot create runner for action "29": charm "facade" relation "provide-juju-dashboard" using a reserved interface: "juju-dashboard"
```

Proposed solution:
juju should refuse to deploy the charm if it has a protected interface