linuxlive 0.4.0: extras

A spec can now carry the distro's own additions, all optional:

• packages: from the base's own archive (apt on Ubuntu, dnf on Fedora).
• files: copied into the system under /etc or /usr (up to 20 MB), with a mode. They can't replace a file linuxlive writes.
• scripts.build: runs as root in the image build, with the network.
• scripts.first-boot: runs once as root on an installed system, before its login screen.
• scripts.first-login: runs once per user, as that user.
• repos: public GitHub code at an exact 40-character commit, with a run command executed in its checkout during the build. Each repo and commit is added to the ISO's package list for the source offer.

Build steps run before linuxlive's own finalize, so branding, the installer and the boot checks still come last and are still tested. The boot check reports every extra. verify-results checks that each package is installed, each file holds the spec's contents and each script ran and succeeded, both in the live session and on the installed disk. The TestOS examples use every kind of extra; run 38542374434 proved all of them on Ubuntu and Fedora.

To upgrade, change @v0.3.0 to @v0.4.0 in your workflow. Specs without extras build exactly as before. See Writing a Spec: Extras.