Nightly builds

What is a nightly run?

CI (continuous integration) team is re-running last passed qt5 integration called as "health check" "nightly built" every night. Those re-runs of already built and passed-all-tests integrations tell us about stability of the build/test system - its form of a benchmark of the "CI health". Experience shows that some of the tests - turn to fail when re-run. Some of then do not even show flaky pattern (i.e. the pattern of "random" pass-fail results) but just fall.

Since those fails - affect the build system (force to rerun, waste-resources) - in case of high number of runs (high impact on build system) - they need special attention - and possibly (fixing) - stabilizing.