In [this PR](https://github.com/localstack/localstack/pull/1200/files) we introduced a new way of starting S3 in a separate process.

In the meantime, the service startup has been significantly reworked, and it seems that we can integrate the S3 starter into the [`multiserver.py`](https://github.com/localstack/localstack/blob/master/localstack/utils/server/multiserver.py) based loading approach that loads multiple APIs in a single process, for performance reasons. We should look into that.
key_by_path = 'key-by-hostname'
        key_by_host = 'key-by-host'
        queue_url, queue_attributes = self._create_test_queue()
        self._create_test_notification_bucket(queue_attributes)
        self.s3_client.put_bucket_versioning(Bucket=TEST_BUCKET_WITH_NOTIFICATION,
                                             VersioningConfiguration={'Status': 'Enabled'})
        
        obj = self.s3_client.put_object(Bucket=TEST_BUCKET_WITH_NOTIFICATION, Key=key_by_path, Body='something')
        
        
        headers = {'Host': '{}.s3.amazonaws.com'.format(TEST_BUCKET_WITH_NOTIFICATION), 'authorization': 'some_token'}
        url = '{}/{}'.format(config.TEST_S3_URL, key_by_host)
        
        response = requests.put(url, data='something else', headers=headers, verify=False)
        self.assertTrue(response.ok)
        self.assertEqual(self._get_test_queue_message_count(queue_url), '2')
        response = self.sqs_client.receive_message(QueueUrl=queue_url)
        messages = [json.loads(to_str(m['Body'])) for m in response['Messages']]
        record = messages[0]['Records'][0]
        self.assertIsNotNone(record['s3']['object']['versionId'])
        self.assertEquals(record['s3']['object']['versionId'], obj['VersionId'])
        
        self.s3_client.put_bucket_versioning(Bucket=TEST_BUCKET_WITH_NOTIFICATION,
                                             VersioningConfiguration={'Status': 'Disabled'})
        self.sqs_client.delete_queue(QueueUrl=queue_url)
        self._delete_bucket(TEST_BUCKET_WITH_NOTIFICATION, [key_by_path, key_by_host])
    def generate_large_file(self, size):