test: increase test coverage for lib/zlib.js

Add tests for constructor behavior and parameter validation. Remove
condition check that cannot be triggered (nothing is greater than
`Infinity`).

PR-URL: https://github.com/nodejs/node/pull/9366


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Minwoo Jung <jmwsoft@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>