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

@@ -18,7 +18,7 @@ get_vm_ip() {
 }
 
 get_vm_name() {
-    echo "libvirt_executor_runner_${CUSTOM_ENV_CI_RUNNER_SHORT_TOKEN}_project-${CUSTOM_ENV_CI_PROJECT_ID}_concurrent_${CUSTOM_ENV_CI_CONCURRENT_PROJECT_ID}"
+    echo "libvirt_executor_runner_${CUSTOM_ENV_CI_RUNNER_SHORT_TOKEN}_project-${CUSTOM_ENV_CI_PROJECT_ID}_job_${CUSTOM_ENV_CI_JOB_ID}"
 }
 
 wait_for_ssh() {