# 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.
host = headers['host']
    return host.startswith(HOSTNAME) or host.startswith(HOSTNAME_EXTERNAL)
def get_bucket_name(path, headers):
    parsed = urlparse.urlparse(path)
    
    bucket_name = parsed.path.split('/')[1]
    
    if uses_path_addressing(headers):
        return normalize_bucket_name(bucket_name)
    
    
    
    common_pattern = re.compile(r'^(.+)\.s3[.\-][a-z]{2}-[a-z]+-[0-9]{1,}'
                                r'\.amazonaws\.com(\.[a-z]+)?$')
    
    
    
    dualstack_pattern = re.compile(r'^(.+)\.s3\.dualstack\.[a-z]{2}-[a-z]+-[0-9]{1,}'
                                   r'\.amazonaws\.com(\.[a-z]+)?$')
    
    
    
    legacy_patterns = re.compile(r'^(.+)\.s3\.?(-external-1)?\.amazonaws\.com(\.[a-z]+)?$')
    
    
    host = headers['host']
    for pattern in [common_pattern, dualstack_pattern, legacy_patterns]:
        match = pattern.match(host)
        if match: