looks like setting ExposeHeaders has no effect on requests to s3 (headers such as `x-amz-version-id` don't reach the clients) for browser-based uploads. 

http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html
import gzip
import json
import os
import requests
import unittest
import uuid
from io import BytesIO
from localstack import config
from localstack.utils.aws import aws_stack
from localstack.utils.common import (
    short_uid, get_service_protocol, to_bytes, safe_requests, to_str, new_tmp_file, rm_rf)
TEST_BUCKET_NAME_WITH_POLICY = 'test_bucket_policy_1'
TEST_BUCKET_WITH_NOTIFICATION = 'test_bucket_notification_1'
TEST_QUEUE_FOR_BUCKET_WITH_NOTIFICATION = 'test_queue_for_bucket_notification_1'
class S3ListenerTest (unittest.TestCase):