Add e2e tests involving live CTest submissions

[williamjallen]

Copied from @zackgalbreath's comment here so it doesn't get lost:

I think this is a good opportunity to add an end-to-end test of CTest with deferred submissions. I started working on this but got sidetracked. Here's some rough pseudocode of how I was imagining this would work:

1. Invalidate DB_DATABASE like we do here
2. Call CTest (either with -D or using a driver script like in the existing "simple" test cases
3. Verify expected behavior: ctest doesn't throw any errors, the XML files land in the inbox, etc.
4. Restore DB_DATABASE and call php artisan submission:queue
5. Verify that the build got parsed successfully.

How to actually achieve this "cleanly" from phpunit is less clear to me. Just a bunch of exec() calls?