0.15.0 Set appropriate AWS ARN for S3 bucket policies in GovCloud

What

• Parameterize the ARN prefix used for S3 bucket policies such that if we are deploying in an AWS GovCloud region, the ARN prefix is arn:aws-us-gov:s3. Otherwise, the ARN prefix is arn:aws:s3.

Why

• These changes allow successful deployment in GovCloud (tested in us-gov-west-1). Prior to this change, attempting to deploy in GovCloud would fail with:

Error: Error putting S3 policy: MalformedPolicy: Policy has invalid resource status code: 400

References

• https://docs.aws.amazon.com/govcloud-us/latest/UserGuide/using-govcloud-arns.html