Don't print token error message when using S3 keys

Version 1.58.1 re-allows any credentials type, but when using S3 keys the following error is printed on stderr:

```
2022/08/19 08:24:16 ERROR : open .token: no such file or directory: IAM - token read error
```
due to first trying with IAM provider and then with keys. The error message is misleading since the process ends successfully, so the message should not be printed when using keys.