test: improve test-crypto-rsa-dsa

* use const and let instead of var
* use assert.strictEqual or assert.strictDeepEqual instead of assert.equal
* use arrow functions
* swap assertions arguments to match the standard
* validate the error for assert.throws

PR-URL: https://github.com/nodejs/node/pull/10681


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