hong kong / ap-east-1

Hey,

This helper doesn't seem to properly support the new regions where the STS stuff isn't global.
I think it's to do with https://docs.aws.amazon.com/cli/latest/reference/sts/ (search for "hong kong" in there).

When using credentials that work in, say, dublin, running the same command in hong kong results in "An error occurred (AuthFailure) when calling the DescribeInstances operation: AWS was not able to validate the provided access credentials" - even thought the region is active and has running instances and so on.