Embed nosync or libeatmydata to CI

We should embed nosync or libeatmydata to the CI and see if we can lower the I/O load on GitLab Runners and make the system test more stable.

Given that it's not clear how to measure system test stability and given the added complexity to the CI, we might want to integrate the change in the CI firsts and then decide if the complexity is worth the gains or remove it otherwise.