Added region as a parameter for aws-mfa.

[shantanugupta]

Regarding the issue(#76), I changed the code. Since I tested when calling sts API without region vs with region. Boto3 resolved to the correct API endpoint when the region was passed. So I made the change to the code to make the package accept region as an additional parameter.

Assumption: .aws/credentials file should contain the region as a required parameter.

[abrockmeyer-govtact]

Please allow this to merge into the repo. I too had this issue for govcloud

[hmoffatt]

This is also needed to work with S3 Multi Region Access Points, which don't work with temporary credentials from the global STS endpoint. https://docs.aws.amazon.com/AmazonS3/latest/userguide/MultiRegionAccessPointRestrictions.html

[hmoffatt]

The commit here is not enough, you must also set the endpoint_url when creating the client. See #52 which has it working.