Fix Host header in http req

[syepes]

The HTTP Host field can not be modified with the standard headers, this make it work

[CLAassistant]

All committers have signed the CLA.

[syepes]

Any news on this merge? I would like to use the official images :-)

[mstoykov]

Hi, sorry @syepes - I don't think anyone specifically looks at this repo at this point :(

After looking at the docs, as I don't really remember the precedence of Host the field, the header and the URL:

// For client requests, Host optionally overrides the Host
// header to send. If empty, the Request.Write method uses
// the value of URL.Host. Host may contain an international
// domain name.

It seems like this is truly needed to overwrite the host in case the header needs to be different from the one that is in the url, so 👍