gitlab_runner: Add VM based executor (libvirt-executor)

For some workloads running in a container is too restrictive, ex:
arch-boxes (loop device, filesystem mount, pacstrap) and archiso
(pacstrap). Currently they both run a TCG accelerated QEMU VM, which is
very slow and painful to work with. We should provide a better option to
our users!

This adds a hardware accelerated VM for this kinds of workloads, which
is way faster and you can do whatever you like (mostly)!

Fix #283

---

TODO:

• Enable KSM?
• Get archiso to build
  • Done: https://gitlab.archlinux.org/klausenbusk/archiso/-/pipelines/10976
• Use BUILD_FAILURE_EXIT_CODE and SYSTEM_FAILURE_EXIT_CODE: https://docs.gitlab.com/runner/executors/custom.html#error-handling
• Fix existing users to use the secure-vm tag

roles/gitlab_runner/files/libvirt-executor-update-base-image

@@ -25,16 +25,14 @@ image=Arch-Linux-x86_64-basic.img
 qemu-img convert -f qcow2 -O raw Arch-Linux-x86_64-basic.qcow2 Arch-Linux-x86_64-basic.img
 
 loopdev="$(losetup --find --partscan --show "${image}")"
-mkdir mnt
-mount "${loopdev}p2" mnt
-mkdir mnt/etc/pacman.d/gnupg
-mount --bind -o ro /etc/pacman.d/gnupg mnt/etc/pacman.d/gnupg
+mount --mkdir "${loopdev}p2" mnt
+mount --mkdir --bind -o ro /etc/pacman.d/gnupg mnt/etc/pacman.d/gnupg
 
 # shellcheck disable=SC2016
 printf 'Server = https://geo.mirror.pkgbuild.com/$repo/os/$arch' > mnt/etc/pacman.d/mirrorlist
 arch-chroot mnt systemctl disable reflector-init
 arch-chroot mnt pacman -Sy --noconfirm --needed archlinux-keyring
-arch-chroot mnt pacman -Syu --noconfirm git git-lfs gitlab-runner
+arch-chroot mnt pacman -Syu --noconfirm --needed git git-lfs gitlab-runner
 sed -E 's/^#(IgnorePkg *=)/\1 linux/' -i mnt/etc/pacman.conf
 arch-chroot mnt userdel -r arch
 mkdir mnt/root/.ssh
@@ -42,7 +40,7 @@ cp /etc/libvirt-executor/id_rsa.pub mnt/root/.ssh/authorized_keys
 chmod 600 mnt/root/.ssh/authorized_keys
 rm -f mnt/etc/machine-id
 
-cp --reflink=always -a mnt/boot/{initramfs-linux-fallback.img,initramfs-linux.img}
+cp -a mnt/boot/{initramfs-linux-fallback.img,initramfs-linux.img}
 
 umount mnt/etc/pacman.d/gnupg
 rmdir mnt/etc/pacman.d/gnupg