# 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.
if not (method == 'POST' and parsed_path.query == 'delete' and '<Delete' in to_str(data or '')):
        return
    content = to_str(response._content)
    if '<Error>' not in content:
        return
    result = xmltodict.parse(content).get('DeleteResult')
    errors = result.get('Error')
    errors = errors if isinstance(errors, list) else [errors]
    deleted = result.get('Deleted')
    if not isinstance(result.get('Deleted'), list):
        deleted = result['Deleted'] = [deleted] if deleted else []
    for entry in list(errors):
        if set(entry.keys()) == set(['Key']):
            errors.remove(entry)
            deleted.append(entry)
    if not errors:
        result.pop('Error')
    response._content = xmltodict.unparse({'DeleteResult': result})
def fix_metadata_key_underscores(request_headers={}, response=None):