support setting S3 region and signature version in stream_io

[lizzzcai]

I am trying to use TensorDeserializer to deserialize the model from aws s3 bucket but getting 400 Bad Request error. However, using TensorSerializer to serialize the model to s3 bucket has no issue.

After some testing, I found that changing the signature_version to s3v4 and setting a proper region_name can make thing work. From aws doc, v2 signature version is deprecated (getting Access Denied), and region is used to overwrite the default value which will point to us-east-1.