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

the S3 wildcard cert is only valid for *.s3.amazonaws.com, not
foo.*.amazonaws.com
[AWS|Storage] add a warning that we've fallen back to path style
Merge pull request #3234 from fcheung/dont_vhost_buckets_with_dots

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