Deleting a non-existent key through s3api's delete-objects should return a valid response..

```
aws s3api delete-objects --bucket my-bucket --delete '{\"Objects\":[{\"Key\":\"my-key\"}]}'
```
Gives...
```
{
    "Deleted": [
        {
            "Key": "my-key"
        }
    ]
}
```

Deleting a non-existent key through s3api's delete-objects on LocalStack returns an error response without any additional information beyond the key.

```
aws s3api delete-objects --bucket my-bucket --delete '{"Objects":[{"Key":"my-key"}]}' --endpoint-url http://localhost:4572
```
Gives...
```
{
    "ResponseMetadata": {
        "HTTPStatusCode": 200,
        "HTTPHeaders": {
            "server": "BaseHTTP/0.6 Python/3.7.5",
            "date": "Fri, 20 Dec 2019 16:02:39 GMT",
            "content-type": "application/xml; charset=utf-8",
            "content-length": "180",
            "access-control-allow-origin": "*",
            "last-modified": "Fri, 20 Dec 2019 16:02:39 GMT",
            "access-control-allow-methods": "HEAD,GET,PUT,POST,DELETE,OPTIONS,PATCH",
            "access-control-allow-headers": "authorization,content-type,content-md5,cache-control,x-amz-content-sha256,x-amz-date,x-amz-security-token,x-amz-user-agent,x-amz-target,x-amz-acl,x-amz-version-id,x-localstack-target,x-amz-tagging",
            "access-control-expose-headers": "x-amz-version-id"
        },
        "RetryAttempts": 0
    },
    "Errors": [
        {
            "Key": "my-key"
        }
    ]
}
```

Deleting an existent key seems to work fine.
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):