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.
keys = keys if isinstance(keys, list) else [keys]
        objects = [{'Key': k} for k in keys]
        self.s3_client.delete_objects(Bucket=bucket_name, Delete={'Objects': objects})
        self.s3_client.delete_bucket(Bucket=bucket_name)
    def _perform_multipart_upload(self, bucket, key, data=None, zip=False, acl=None):
        kwargs = {'ACL': acl} if acl else {}
        multipart_upload_dict = self.s3_client.create_multipart_upload(Bucket=bucket, Key=key, **kwargs)
        uploadId = multipart_upload_dict['UploadId']
        
        data = data or (5 * short_uid())
        data = to_bytes(data)
        upload_file_object = BytesIO(data)
        if zip:
            upload_file_object = BytesIO()
            with gzip.GzipFile(fileobj=upload_file_object, mode='w') as filestream:
                filestream.write(data)
        response = self.s3_client.upload_part(Bucket=bucket, Key=key,
            Body=upload_file_object, PartNumber=1, UploadId=uploadId)
        multipart_upload_parts = [{'ETag': response['ETag'], 'PartNumber': 1}]
        return self.s3_client.complete_multipart_upload(Bucket=bucket,
            Key=key, MultipartUpload={'Parts': multipart_upload_parts}, UploadId=uploadId)
    def _perform_presigned_url_upload(self, bucket, key):
        url = self.s3_client.generate_presigned_url(
            'put_object', Params={'Bucket': bucket, 'Key': key}
        )
        url = url + '&X-Amz-Credential=x&X-Amz-Signature=y'
        requests.put(url, data='something', verify=False)