`multipass restart` should just start instances if they're not running

Steps:
- launch an instance
- stop it or suspend
- try to `restart` it

Expected:
- instance gets started

Current:
- error:
```
restart failed: instance "preferable-phoenix" is not running
```

Start by reproducing the reported sequence with the `multipass` CLI: launch an instance, stop or suspend it, then run `multipass restart`. Trace the restart command from that entry point and verify that a stopped or suspended instance is started without the current not-running error.

Written by the indexing model from the issue text.