URL already in use, but cannot update

`ckanapi load datasets` without `-o`:
```
1 [None] --- create ValidationError {"__type":"Validation Error","name":["That URL is already in use."]}
```

`ckanapi load datasets` with`-o`:
```
1 [None] --- show NotFound [null,"protocol-plant-measurements-in-heath-and-meadow-sites_v1"]
```