test: improve code in test-fs-readfile-error

* use const instead of var
* use common.mustCall to control the functions execution automatically
* use assert.strictEqual instead of assert.equal
* use assert.notStrictEqual instead of assert.notEqual
* use arrow functions

PR-URL: https://github.com/nodejs/node/pull/10367


Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>