Ignore Body of Responses to HEAD Requests as per Spec

[gkleen]

As per the HTTP Spec server responses to HEAD Requests must not contain bodies.

Nontheless minio-hs relies on the existence of a Content-Type header as a heuristic of whether to expect an error message in the body of the response.
Some S3 api servers (such as garage adhere to the http spec and produce responses to HEAD requests without bodies but containing a Content-Type header (because an analogous GET request would return one). minio-hs currently fails in such situations.

[donatello]

@gkleen Could you rebase your PR on master branch so that we can run the updated tests?

[gkleen]

@gkleen Could you rebase your PR on master branch so that we can run the updated tests?

Sorry for the late reply, I'm quite busy with teaching and work

Did the rebase, though.