# 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.
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):
    result = {'Error': {'Code': code, 'Message': message}}
    content = xmltodict.unparse(result)
    headers = {'content-type': 'application/xml'}
    return requests_response(content, status_code=status_code, headers=headers)
def no_such_key_error(resource, requestId=None, status_code=400):
    result = {'Error': {'Code': 'NoSuchKey',
            'Message': 'The resource you requested does not exist',
            'Resource': resource, 'RequestId': requestId}}
    content = xmltodict.unparse(result)
    headers = {'content-type': 'application/xml'}
    return requests_response(content, status_code=status_code, headers=headers)
def token_expired_error(resource, requestId=None, status_code=400):
    result = {'Error': {'Code': 'ExpiredToken',
            'Message': 'The provided token has expired.',
            'Resource': resource, 'RequestId': requestId}}
    content = xmltodict.unparse(result)
    headers = {'content-type': 'application/xml'}
    return requests_response(content, status_code=status_code, headers=headers)
def expand_redirect_url(starting_url, key, bucket):