tests/18-upgrade: Remove quantal and raring tests

They are gone. Forever. :-(
saucy unsupported, add utopic

Still disappointed they didn't choose undead unicorn as codename...
tests/18-upgrade: install x11 instead of xephyr

x11 pulls in xorg, that sometimes installs alternative xorg lts packages.
xephyr does not fetch anything from mirrors anymore.
Merge pull request #934 from drinkcat/remove-quantal-raring-test

tests/18-upgrade: Remove quantal and raring tests