Add maintenance cron scripts

cron.hourly/README.md

+# Maintenance cron scripts
+
+Following scripts belong to `/etc/cron.daily/` (or similar, at your
+discretion) on a GitLab Runner, where this repository is cloned.
+
+## Script description
+
+- `gitlab-runner-libvirt-qemu-pull-images`
+
+Runs `libvirt-qemu/pull-images.sh` script, which pulls and extracts
+QCOW2 images to the GitLab Runner.
+
+- `pull-gitlab-runner-scripts-repo`
+
+Pull this repository to deploy changes to Custom executor.

cron.hourly/gitlab-runner-libvirt-qemu-pull-images

+#!/bin/sh
+
+exec /home/gitlab-runner/gitlab-runner-scripts/libvirt-qemu/pull-images.sh > /dev/null 2>&1

cron.hourly/pull-gitlab-runner-scripts-repo

+#!/bin/sh
+
+cd /home/gitlab-runner/gitlab-runner-scripts && git pull > /dev/null 2>&1