test: refactor and fix test-crypto

* var -> const.
* Group and sort imports.
* Replace use of the deprecated crypto.createCredentials.
* Fix incorrect use of string instead of RegExp in `throws` assertions.
* Clone array with `.slice()` and remove dependency on util.
* assert.notEqual -> assert.notStrictEqual.
* indexOf -> includes.

PR-URL: https://github.com/nodejs/node/pull/9807


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>