when I try to upload a large file, localstack basically freezes (and eventually times out).  
But if the file is all `1` bytes it succeeds.

succeeds:
```bash
aws s3 --endpoint-url=http://localhost:4572 mb s3://testbucket
python -c "print '\x01'*10000000" > testfile
echo $(ls -ahl | grep testfile)
aws s3 --endpoint-url=http://localhost:4572 cp testfile s3://testbucket/testfile
```

fails:
```bash
aws s3 --endpoint-url=http://localhost:4572 mb s3://testbucket
python -c "print 'a'*10000000" > testfile
echo $(ls -ahl | grep testfile)
aws s3 --endpoint-url=http://localhost:4572 cp testfile s3://testbucket/testfile
```
so, for me, both the file content and its size determine if this triggers or not. 
I'm using the latest version `0.9.5`
bucket_name = 'test-bucket-%s' % short_uid()
        self.s3_client.create_bucket(Bucket=bucket_name)
        body = 'something body'
        
        object_key = 'test-presigned-post-key'
        presigned_request = self.s3_client.generate_presigned_post(
            Bucket=bucket_name,
            Key=object_key
        )
        
        files = {'file': body}
        response = requests.post(presigned_request['url'], data=presigned_request['fields'], files=files, verify=False)
        self.assertEqual(response.status_code, 200)
        
        downloaded_object = self.s3_client.get_object(Bucket=bucket_name, Key=object_key)
        download_object = downloaded_object['Body'].read()
        self.assertEqual(to_str(body), to_str(download_object))
        
        self._delete_bucket(bucket_name, [object_key])
    def test_s3_delete_response_content_length_zero(self):