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)
        
        object_key = 'key-by-hostname'
        self.s3_client.put_object(Bucket=bucket_name, Key=object_key, Body='something')
        self.s3_client.put_bucket_cors(Bucket=bucket_name,
            CORSConfiguration={
                'CORSRules': [{
                    'AllowedMethods': ['GET', 'PUT', 'POST'],
                    'AllowedOrigins': ['*'],
                    'ExposeHeaders': [
                        'ETag', 'x-amz-version-id'
                    ]
                }]
            },
        )
        
        url = self.s3_client.generate_presigned_url(
            'get_object', Params={'Bucket': bucket_name, 'Key': object_key}
        )
        response = requests.get(url, verify=False)
        self.assertEquals(response.headers['Access-Control-Expose-Headers'], 'ETag,x-amz-version-id')
        
        self._delete_bucket(bucket_name, [object_key])
    def test_s3_get_response_header_overrides(self):