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.assertNotIn(version_id, object_versions)
        
        self.s3_client.put_bucket_versioning(Bucket=TEST_BUCKET_WITH_VERSIONING,
                                             VersioningConfiguration={'Status': 'Disabled'})
        self._delete_bucket(TEST_BUCKET_WITH_VERSIONING, [test_1st_key, test_2nd_key])
    
    
    
    def _create_test_queue(self):
        queue_url = self.sqs_client.create_queue(QueueName=TEST_QUEUE_FOR_BUCKET_WITH_NOTIFICATION)['QueueUrl']
        queue_attributes = self.sqs_client.get_queue_attributes(QueueUrl=queue_url, AttributeNames=['QueueArn'])
        return queue_url, queue_attributes
    def _create_test_notification_bucket(self, queue_attributes):
        self.s3_client.create_bucket(Bucket=TEST_BUCKET_WITH_NOTIFICATION)
        self.s3_client.put_bucket_notification_configuration(
            Bucket=TEST_BUCKET_WITH_NOTIFICATION,
            NotificationConfiguration={
                'QueueConfigurations': [
                    {
                        'QueueArn': queue_attributes['Attributes']['QueueArn'],
                        'Events': ['s3:ObjectCreated:*']
                    }
                ]
            }
        )
    def _get_test_queue_message_count(self, queue_url):
        queue_attributes = self.sqs_client.get_queue_attributes(
            QueueUrl=queue_url, AttributeNames=['ApproximateNumberOfMessages'])
        return queue_attributes['Attributes']['ApproximateNumberOfMessages']
    def _delete_bucket(self, bucket_name, keys=[]):