Introduce a waitForScripting helper function and use it in all scri…

…pting integration tests

Code inspection uncovered that quite a few integration tests don't wait
for scripting to be ready before proceeding, which is a source of
intermittent failures, especially on slower machines where e.g. creating
the sandbox takes longer.

This commit fixes the issues by introducing a `waitForScripting` helper
function and calling it consistently in all scripting integration tests.