Changes:
- order groups alphabetically
- use the same comment "Ensure those groups exist" consistently in the 2
scripts, and also drop the comment regarding a "generically named"
function.
- adds "|| true" to the usermod command in kali-user-setup (only for
consistency, the script is not run with "set -e" anyway).
After those changes, the two functions "configure_usergroups()" are very
similar, and it's very easy to spot the differences between both.