test: refactor test-http-response-statuscode

* move repeated code to function
* use strings for expected error (exposes result for [] as empty string)
* remove unneeded `common.mustCall()` usage with function arguments that
  are not callbacks

PR-URL: https://github.com/nodejs/node/pull/11274


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>