test: refactor test-crypto-random

* specify constructor for assert.throws()
* load additional modules only if crypto check passes
* normalize some potentially confusing indentation
* provided actual first and expected second in assertions

PR-URL: https://github.com/nodejs/node/pull/10232


Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>