[Bug] Access-Control-Allow-Origin:* not present in 404 response headers

[samuel-belcastro]

To reproduce:

1. Send a HEAD request to a fake-s3 bucket file that does exist from a different origin than the bucket. Check the response headers and verify Access-Control-Allow-Origin:* is present.
2. Send a HEAD request to a fake-s3 bucket file that does not exist from a different origin than the bucket. Access-Control-Allow-Origin:* is not present in the response headers.

[samuel-belcastro]

@jubos I have a fix for GET and HEAD requests. If you see this as an important issue, let me know and I'll create a pull request and do the testing. Otherwise you can close this, and I will use my fork.

[jubos]

Seems like a worthwhile fix, let me know when you have your diff ready.

[samuel-belcastro]

Diff is ready: https://github.com/jubos/fake-s3/pull/217

Please let me know when you are able to get this merged in.