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. 
key_by_path = 'key-by-hostname'
        queue_url, queue_attributes = self._create_test_queue()
        self._create_test_notification_bucket(queue_attributes)
        
        self._perform_multipart_upload(bucket=TEST_BUCKET_WITH_NOTIFICATION, key=key_by_path, zip=True)
        self.assertEqual(self._get_test_queue_message_count(queue_url), '1')
        
        self.sqs_client.delete_queue(QueueUrl=queue_url)
        self._delete_bucket(TEST_BUCKET_WITH_NOTIFICATION, [key_by_path])
    def test_s3_multipart_upload_acls(self):
        bucket_name = 'test-bucket-%s' % short_uid()
        self.s3_client.create_bucket(Bucket=bucket_name, ACL='public-read')
        def check_permissions(key, expected_perms):
            grants = self.s3_client.get_object_acl(Bucket=bucket_name, Key=key)['Grants']
            grants = [g for g in grants if 'AllUsers' in g.get('Grantee', {}).get('URI', '')]
            self.assertEquals(len(grants), 1)
            permissions = grants[0]['Permission']
            permissions = permissions if isinstance(permissions, list) else [permissions]
            self.assertEquals(len(permissions), expected_perms)
        
        self.s3_client.put_object(Bucket=bucket_name, Key='acl-key0', Body='something')
        check_permissions('acl-key0', 1)
        self._perform_multipart_upload(bucket=bucket_name, key='acl-key1')
        check_permissions('acl-key1', 1)
        self._perform_multipart_upload(bucket=bucket_name, key='acl-key2', acl='public-read-write')
        check_permissions('acl-key2', 2)
    def test_s3_presigned_url_upload(self):