[AWS|S3] Vhost buckets don't work if bucket name has a . in it

We shouldn't convert to dns addresseing in this case since the S3 wildcard cert is only valid for \*.s3.amazonaws.com, not foo.\*.amazonaws.com. 
Should we still warn as well, but with a warning more clearly about this edge? Seems like it might be good to let people know (since at least historically it caused a noticeable performance impact to use path style instead).