Create disk, containing updates.img in createhdds.sh, also modularize
it a little bit.
Since openqa_fedora repo now contains VARIABLES.md
file that includes all relevant variables, QEMU_variables.txt is
no longer needed and could confuse someone.
Another change is with REPOSITORY_GRAPHICAL and REPOSITORY_VARIATION
variables - current instructions on how to set them were out of date.
If you're going to change this you should also change the fedup test in templates (where this image is used). It's only used for a known-broken fedup test, but still, it doesn't make any sense for them not to line up (and I guess we'll build the new-upgrade-mechanism tests from the charred remains of the fedup tests, so we probably want to keep them in order).