handle BucketAlreadyOwnedByYou when storing xarray Dataset
handle BucketAlreadyOwnedByYou when storing xarray Dataset

When attempting to store an xarray `Dataset` in zarr format into my own
minio object-store I was getting the exception BucketAlreadyOwnedByYou
from botocore even though the `makedirs` called had `exist_ok=True`.
Looking at the s3fs source-code it appears this situation wasn't handled
before, but it is now.

fsspec/s3fs