ElementaryOS an Ubuntu focal deriveted

Just little changes to adapt eggs to ElementaryOS, mostly inserted Elementary in distro.ts, changed the way bash-completion is installed (now we try both this path: /etc/bash-completion.d and /usr/share/bash-completion/Completions where this distro want bash-completion scripts) , and a little bugfix for lightdm.conf, don't fail if don't find it, but build a minimun lightdm.conf)