Scheduling a build should allow force disabling test phase

My use case is to schedule a precheck to build all of qt5.git using some specific qt5 change ref, but without running tests.

I want to check that there are no build regressions, but I don't care about running tests, and that will significantly decrease precheck time.

Currently there is a Force testrun checkbox.

We could add a new Disable testrun checkbox, which will likely just append "donotruntests" feature to all platform configurations, so it does not generate test items.

Care must be taken so that it does not cause a full rebuild unless needed, aka make the option cache friendly.
E.g. if i schedule a custom qt5.git change that just updates the submodule sha1 for webengine, i want qtbase, declarative and friends to re-use the cached artifacts.