test: refactor test-cli-eval.js

* assert unused vars in test-cli-eval.js
* assert in more idiomatic way test-cli-eval
* rename status to err in test-cli-eval.js

PR-URL: https://github.com/nodejs/node/pull/10759


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>