Throw an exception when testing non response body in javascript tests

Problem/Motivation

In potential preparation of #2775653: JavascriptTests with webDriver we need to ensure that calling to statusCodeEquals() and responseHeaderEquals().

Given that

I think we should do a hard break on statusCodeEquals and throw an exception JTB is experimental and supporting multiple versions is way more expensive. We could change drupalLogin to not use it but assert something else or just remove it since if the form fails it fails.

Proposed resolution

Add the exceptions

Remaining tasks

Write a quick change record for it.

User interface changes

API changes

Data model changes