Report invalid --require directly instead of via UnhandledPromiseRejectionWarning

[Krinkle]

• QUnit version: 2.18.2
• Which environment are you using?: Node.js
• How are you running QUnit?: QUnit CLI

We have a test case displays helpful error when failing to require a file in test/cli/cli-main.js which. The assertion currently ensures that the output "includes" the important subset, which is Error: Cannot find module 'does-not-exist-at-all'.

However, when running it directly (in prep for #1684) I noticed it gets there in quite an unsual manner:

(node:4519) UnhandledPromiseRejectionWarning: Error: Cannot find module 'does-not-exist-at-all'
Require stack:
- /qunit/src/cli/require-from-cwd.js
- /qunit/src/cli/run.js
- /qunit/bin/qunit.js
    at internal
    at bin/qunit
    at internal
    at bin/qunit
    at internal
(node:4519) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:4519) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

This happens because /src/cli/run.js currently handles options.requires before setting up options.reporter and process.on('unhandledRejection'). I suggest we swap this around.