More basic system tests

[NeQuissimus]

• sysctl: Check that boot.kernel.sysctl commands are properly applied
• kernelParams: Ensure boot.kernelParams are applied
• environment: Create file directly in /etc and one in sub-directories and verify structure/content, environment.sessionVariables should show up in the environment

I declared all three of them release-blocking

[mention-bot]

@NeQuissimus, thanks for your PR! By analyzing the history of the files in this pull request, we identified @edolstra, @aszlig and @peti to be potential reviewers.