Start httpd synchronously

This ensures that when "start httpd" returns, Apache is actually
listening.

http://hydra.nixos.org/build/5499393
Give more memory to the KDE test

http://hydra.nixos.org/build/5499387
Fix the rebuildCD test

http://hydra.nixos.org/build/5500743
Remove outdated comment

Password-based remote root logins are not allowed anyway.
Fix the sshd check in the rebuildCD test

Also reduce the amount of memory.