Internal k6 objects aren't properly encoded to JSON

[na--]

Most of the internal Go objects that are passed to the script like http.Response aren't marshalled to JSON properly, the Go structs simply lack the appropriate js tags. This is especially problematic when they are returned as part of a setup() result, since it is passed through JSON before the VUs and teardown() receive it. I've briefly mentioned about this in the comments of #558 and #693, but since they've been mostly closed by #799, I'm creating this separate issue just for this bug.

To demonstrate, this script:

import http from "k6/http";

export function setup() {
   return http.get("https://test.loadimpact.com");
}

export default function (data) {
   let resp = http.get("https://test.loadimpact.com");

   console.log(Object.keys(data))
   console.log(Object.keys(resp))
}

will output something like this:

INFO[0002] Headers,OCSP,Body,TLSVersion,Request,RemoteIP,RemotePort,TLSCipherSuite,Error,Proto,Cookies,Timings,URL,Status 
INFO[0002] remote_ip,remote_port,url,status,proto,headers,cookies,body,timings,tls_version,tls_cipher_suite,ocsp,error,request,clickLink,html,json,submitForm

[mstoykov]

fixed by #804