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. 
self.s3_client.create_bucket(Bucket=TEST_BUCKET_NAME_WITH_POLICY)
        
        policy = {
            'Version': '2012-10-17',
            'Statement': {
                'Action': ['s3:GetObject'],
                'Effect': 'Allow',
                'Resource': 'arn:aws:s3:::bucketName/*',
                'Principal': {
                    'AWS': ['*']
                }
            }
        }
        response = self.s3_client.put_bucket_policy(
            Bucket=TEST_BUCKET_NAME_WITH_POLICY,
            Policy=json.dumps(policy)
        )
        self.assertEqual(response['ResponseMetadata']['HTTPStatusCode'], 204)
        
        saved_policy = self.s3_client.get_bucket_policy(Bucket=TEST_BUCKET_NAME_WITH_POLICY)['Policy']
        self.assertEqual(json.loads(saved_policy), policy)
    def test_s3_put_object_notification(self):