ensure kv store is initialized when saving states (#10559)
ensure kv store is initialized when saving states (#10559)

* ensure kv store is initialized when saving states

Currently, if you call `save_states()` on newly created trainer:
```
>       if self._update_on_kvstore:
E       AttributeError: 'Trainer' object has no attribute '_update_on_kvstore'
```

* zap trailing whitespace

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