CI: streamline packet jobs definition

- Take advantage of `parallel:matrix` to make the jobs definition shorter
  and more readable.
- Remove helper scripts which are no longer needed
- Remove redundant indirection in the gitlab-ci pipelines definitions
  (only one user)

tests/files/opensuse15-6-docker-cilium.yml

@@ -0,0 +1,10 @@
+---
+# Instance settings
+cloud_image: opensuse-leap-15-6
+
+# Kubespray settings
+kube_network_plugin: cilium
+
+# Docker specific settings:
+container_manager: docker
+etcd_deployment_type: docker