azure: Change all S3 URLs in our CI to use subdomains

Old S3 URLs are used all across our CI scripts and [they're going to be deprecated](https://aws.amazon.com/blogs/aws/amazon-s3-path-deprecation-plan-the-rest-of-the-story/). We should switch all of `s3.amazonaws.com/bucket` to `bucket.s3.amazonaws.com`.