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`
filename = 'large_file_%s' % uuid.uuid4()
        f = open(filename, 'wb')
        f.seek(size - 1)
        f.write(b'\0')
        f.close()
        return open(filename, 'r')
    def test_s3_upload_fileobj_with_large_file_notification(self):