Hi!

I have noticed that today (25th of Feb) a new version of localstack docker image was pushed to the repository (82c83ff027114060938856eac5dc7be1d534afd0b7711510246de4a76dde2396) and this version fails in my integration tests with an exception:

```
2020-02-25T12:09:44:ERROR:localstack.services.generic_proxy: Error forwarding request: An error occurred (404) when calling the HeadObject operation: Not Found Traceback (most recent call last):
  File "/opt/code/localstack/localstack/services/generic_proxy.py", line 303, in forward updated_response = self.proxy.update_listener.return_response(**kwargs)
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 954, in return_response
send_notifications(method, bucket_name, object_path, version_id)
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 178, in send_notifications
send_notification_for_subscriber(notif, bucket_name, object_path,
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 191, in send_notification_for_subscriber
object_size = s3_client.head_object(Bucket=bucket_name, Key=key).get('ContentLength', 0)
  File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 316, in _api_call
return self._make_api_call(operation_name, kwargs)
  File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 626, in _make_api_call
  raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (404) when calling the HeadObject operation: Not Found
```
The same setup in docker-compose works with version 0.10.7 and 0.10.6 without any errors or exceptions. 
bucket_name = 'test-bucket-%s' % short_uid()
        key = 'test.file'
        hostname_before = config.HOSTNAME_EXTERNAL
        config.HOSTNAME_EXTERNAL = 'foobar'
        try:
            content = 'test content 123'
            acl = 'public-read'
            self.s3_client.create_bucket(Bucket=bucket_name)
            
            response = self._perform_multipart_upload(bucket=bucket_name, key=key, data=content, acl=acl)
            expected_url = '%s://%s:%s/%s/%s' % (get_service_protocol(), config.HOSTNAME_EXTERNAL,
                config.PORT_S3, bucket_name, key)
            self.assertEqual(expected_url, response['Location'])
            
            self.s3_client.put_object_acl(Bucket=bucket_name, Key=key, ACL=acl)
            
            downloaded_object = self.s3_client.get_object(Bucket=bucket_name, Key=key)
            self.assertEqual(to_str(downloaded_object['Body'].read()), content)
            
            download_url = response['Location'].replace('%s:' % config.HOSTNAME_EXTERNAL, 'localhost:')
            response = safe_requests.get(download_url)
            self.assertEqual(response.status_code, 200)
            self.assertEqual(to_str(response.content), content)
        finally:
            config.HOSTNAME_EXTERNAL = hostname_before
    def test_s3_website_errordocument(self):