Automatically determine region & hence S3 endpoint of buckets

Use getBucketLocation to determine location & map to endpoint, if fs.s3a.endpoint is set to "automatic"

S3guard added the API call String getBucketLocation(), which is used for DDB binding, We can also use this to determine the s3 endpoint, to avoid recurrent issues with auth failures related to it not being valid

Still need to handle: buckets on third-party servers, and the inevitability that new AWS regions will be added after the Hadoop version & AWS Jar is shipped and frozen