The form POST operation to S3 accepts a `success_action_status` field which can be set to 200/201/204, see [here](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html). Localstack currently handles the `success_action_redirect` field [here](https://github.com/localstack/localstack/blob/master/localstack/services/s3/s3_listener.py#L518) and so we should look into handling the `success_action_status` field too.

The 201 from AWS responds with an XML document with some fields about the object that has just been created in AWS, see below.

```
<PostResponse>
    <Location>https://s3.amazonaws.com/link-to-the-file</Location>
    <Bucket>s3-bucket</Bucket>
    <Key>development/8614bd40-691b-4668-9241-3b342c6cf429/image.jpg</Key>
    <ETag>"32-bit-tag"</ETag>
</PostResponse>
```
"""Tests for the existence of the specified bucket. Returns the error code
    if the bucket does not exist (200 if the bucket does exist).
    """
    bucket_name = normalize_bucket_name(bucket_name)
    s3_client = aws_stack.connect_to_service('s3')
    try:
        s3_client.head_bucket(Bucket=bucket_name)
    except ClientError as err:
        error_code = err.response.get('Error').get('Code')
        return False, error_code
    return True, 200
def check_content_md5(data, headers):
    actual = md5(strip_chunk_signatures(data))
    expected = headers['Content-MD5']
    try:
        expected = to_str(codecs.encode(base64.b64decode(expected), 'hex'))
    except Exception:
        expected = '__invalid__'
    if actual != expected:
        return error_response('The Content-MD5 you specified was invalid', 'InvalidDigest', status_code=400)
def error_response(message, code, status_code=400):