Adding ram only, shared func for init, ubuntu version as variable and secure boot

...s/config/02-customisation/etc/initramfs-tools/scripts/pxe

...config/02-customisation/etc/initramfs-tools/scripts/tools

live_exam_os/config/02-customisation/home/user/.profile

live_exam_os/config/03-post_install/2500-disable_services.sh

live_exam_os/config/03-post_install/3000-nexus_exam.sh

live_exam_os/config/03-post_install/5000-push_challenge.sh

live_exam_os/config/03-post_install/5000-pxe.sh

live_exam_os/config/03-post_install/8000-initramfs.sh

live_exam_os/config/03-post_install/9999-cleanup.sh

live_exam_os/tools/functions.sh