WIP: handle missing builds for tests when scheduling jobs

[lbarcziova]

This is an alternative WIP solution for #2399

With this, the behaviour of /packit test will not change, but I do not like that we have to handle this logic "manually" in jobs.py. (Previously we handled this in TestingFarmHandler, but that lead to the race condition as there can be multiple test jobs => multiple TestingFarmHandler runs where each scheduled the Copr build job if there was a missing builds. We also cannot easily handle this in CoprBuildHandler, as on the other hand, there, we do not know which test jobs should be taken into consideration)

RELEASE NOTES BEGIN

TODO

RELEASE NOTES END

[sentry-io[bot]]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: packit_service/worker/jobs.py

Function	Unhandled Issue
create_tasks	KeyError: 'upstream_pkg_name' task.steve_jobs.pro... Event Count: 1

---

_{Did you find this useful? React with a 👍 or 👎}

[softwarefactory-project-zuul[bot]]

Build failed. https://softwarefactory-project.io/zuul/t/packit-service/buildset/df910a364f02496fbe0bdca87c05efef

:heavy_check_mark: pre-commit SUCCESS in 2m 13s :x: packit-service-tests FAILURE in 2m 26s