arrow

ARROW-13685: [C++] Cannot write dataset to S3FileSystem if bucket already exists

I still need to add a regression test.  I've been able to test by configuring my server with minio client.  I think it'd probably be easiest to create a crossbow test for this situation.  Current steps:

```
mc alias set myminio http://localhost:9000 minioadmin minioadmin
mc admin policy add myminio/ no-create-buckets ci/etc/minio-no-create-bucket-policy.json
mc admin user add myminio/ limited limited123
mc admin policy set myminio no-create-buckets user=limited
mc mb myminio/existing-bucket
```

Then, in python:

```
import pyarrow.fs as fs
filesystem = fs.S3FileSystem(access_key='limited', secret_key='limited123', endpoint_override='http://localhost:9000')
filesystem.create_dir('existing-bucket/foo') # This line fails without the change
```

Closes #11136 from westonpace/bugfix/ARROW-13685-cannot-write-to-s3-if-bucket-exists

Authored-by: Weston Pace <weston.pace@gmail.com>
Signed-off-by: Weston Pace <weston.pace@gmail.com>