# Type of request: This is a bug report

# Detailed description
S3 list buckets returns a different format for CreationDate than the one expected by the Java SDK and parsing fails. Using Java SDK 2.13.39. Also verified w/ .40, .38, .30 and .20. Will check previous Docker releases for localstack.

``Unable to unmarshall response (Text '2020-06-17T15:26:46.032838+00:00' could not be parsed at index 19). Response Code: 200, Response Text: 
software.amazon.awssdk.core.exception.SdkClientException: Unable to unmarshall response (Text '2020-06-17T15:26:46.032838+00:00' could not be parsed at index 19). Response Code: 200, Response Text: <truncated...>
``

## Expected behavior
Return CreationDate in same format as the actual S3 API call.

## Actual behavior
Returns CreationDate in slightly different format from the actual S3 API call. Fractional seconds are included.

# Steps to reproduce
Run "aws s3api list-buckets" vs "aws s3api list-buckets --endpoint-url http://localstack:4566" and note different date format for CreationDate.

## Command used to start LocalStack
docker-compose:
```
  localstack:
    image: localstack/localstack
    ports:
      - '4566:4566'
    environment:
      SERVICES: s3
      DEBUG: 1
```
## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
See steps to reproduce.
return 'x-amz-copy-source' in headers or 'x-amz-copy-source' in path
    @staticmethod
    def get_201_response(key, bucket_name):
        return """
                <PostResponse>
                    <Location>{protocol}://{host}/{encoded_key}</Location>
                    <Bucket>{bucket}</Bucket>
                    <Key>{key}</Key>
                    <ETag>{etag}</ETag>
                </PostResponse>
                """.format(
            protocol=get_service_protocol(),
            host=config.HOSTNAME_EXTERNAL,
            encoded_key=urlparse.quote(key, safe=''),
            key=key,
            bucket=bucket_name,
            etag='d41d8cd98f00b204e9800998ecf8427f',
        )
    @staticmethod
    def _update_location(content, bucket_name):
        bucket_name = normalize_bucket_name(bucket_name)
        host = config.HOSTNAME_EXTERNAL
        if ':' not in host:
            host = '%s:%s' % (host, config.PORT_S3)
        return re.sub(r'<Location>\s*([a-zA-Z0-9\-]+)://[^/]+/([^<]+)\s*</Location>',
                      r'<Location>%s://%s/%s/\2</Location>' % (get_service_protocol(), host, bucket_name),
                      content, flags=re.MULTILINE)
    @staticmethod
    def is_query_allowable(method, query):