[REF] 8.0 mgmtsystem_action

The current module inherit `crm.claim` while the `state` attribute doesn't exist anymore. I made some changes to use the `stage_id` instead but I'm not so sure it's a good idea. I'm open to suggestions.
Only a style suggestion, but this is nicer to format:
```
             values['stage_id'] = self.stage_find(
                 self, None, [('name', '=', 'In Progress')]
             )