test: improve test-fs-write-stream-throw-type

* validate the errors for all assert.throws
* use arrow functions

PR-URL: https://github.com/nodejs/node/pull/10779


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>