This also allows to restrict the error message to the actual error message.
before:
```
$ swh deposit metadata-only --url http://localhost:5080/deposit \
--username test \
--password test2 \ # wrong creds
--metadata ../deposit-swh.update-metadata.xml
{"summary": "401: b'{\"error\":\"invalid_grant\",\"error_description\":\"Invalid user credentials\"}'", "detail": "", "sword:verboseDescription": "API is protected by basic authentication", "swh:deposit_id": null, "swh:deposit_status": null, "status": 401}
```
With the following diff:
```
ERROR:swh.deposit.cli.client:Problem during parsing options: Service document retrieval: {"error":"invalid_grant","error_description":"Invalid user credentials"}
```