Workaround for invoking GatlingConfiguration.setUpForTest

Your serialization issue causing core dumps (caused by mocks) happens because you use incomplete mocks reporting is not disabled.

Gatling has a special method for setting up config for tests and disabling reporting, but it's private for now (see https://github.com/gatling/gatling/issues/2326). This workaround introduces a public entry point in io.gatling package.