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()
        self.s3_client.create_bucket(Bucket=bucket_name)
        
        object_key = 'key-by-hostname'
        self.s3_client.put_object(Bucket=bucket_name, Key=object_key, Body='something')
        
        url = self.s3_client.generate_presigned_url(
            'get_object', Params={
                'Bucket': bucket_name,
                'Key': object_key,
                'ResponseCacheControl': 'max-age=74',
                'ResponseContentDisposition': 'attachment; filename="foo.jpg"',
                'ResponseContentEncoding': 'identity',
                'ResponseContentLanguage': 'de-DE',
                'ResponseContentType': 'image/jpeg',
                'ResponseExpires': 'Wed, 21 Oct 2015 07:28:00 GMT'}
        )
        response = requests.get(url, verify=False)
        self.assertEqual(response.headers['cache-control'], 'max-age=74')
        self.assertEqual(response.headers['content-disposition'], 'attachment; filename="foo.jpg"')
        self.assertEqual(response.headers['content-encoding'], 'identity')
        self.assertEqual(response.headers['content-language'], 'de-DE')
        self.assertEqual(response.headers['content-type'], 'image/jpeg')
        self.assertEqual(response.headers['expires'], '2015-10-21T07:28:00Z')
        
        self._delete_bucket(bucket_name, [object_key])
    def test_s3_copy_md5(self):