Re-run Amazon tests in us-standard

[gaul]

Amazon clarified their consistency model:

https://docs.aws.amazon.com/AmazonS3/latest/dev/Introduction.html#ConsistencyModel

Note that read-after-write is more complicated if you read-after-write-after-read, according to a Hacker News comment:

https://news.ycombinator.com/item?id=12922048

[pragnesh]

us-standard region also support read-after-write consistency according to this link https://aws.amazon.com/about-aws/whats-new/2015/08/amazon-s3-introduces-new-usability-enhancements/

[gaul]

Related to #18.