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)
        
        src_key = 'src'
        self.s3_client.put_object(Bucket=bucket_name, Key=src_key, Body='something')
        
        dest_key = 'dest'
        response = self.s3_client.copy_object(Bucket=bucket_name, CopySource={'Bucket': bucket_name, 'Key': src_key},
                                              Key=dest_key)
        self.assertEqual(response['ResponseMetadata']['HTTPStatusCode'], 200)
        
        dest_key2 = 'dest'
        url = self.s3_client.generate_presigned_url(
            'copy_object', Params={'Bucket': bucket_name, 'CopySource': {'Bucket': bucket_name, 'Key': src_key},
                                   'Key': dest_key2}
        )
        
        request_response = requests.put(url, verify=False, headers={'Content-MD5': 'ignored_md5'})
        self.assertEqual(request_response.status_code, 200)
        
        self._delete_bucket(bucket_name, [src_key, dest_key, dest_key2])
    def test_s3_invalid_content_md5(self):