Split deploy steps in separate playbooks: part1 (#3451)

* Fix bootstrap_os/ubuntu idempotency

* Update bastion role

* move container_engine in sub-roles

* requires ansible 2.5

* ubuntu18 as first CI job

roles/container-engine/rkt/tasks/main.yml

@@ -0,0 +1,13 @@
+---
+- name: Install rkt
+  import_tasks: install.yml
+  when: not ansible_os_family in ["CoreOS", "Container Linux by CoreOS"]
+
+- name: Set up cron job to do garbage cleanup
+  copy:
+    src: rkt-gc.sh
+    dest: /etc/cron.hourly/rkt-gc.sh
+    owner: root
+    group: root
+    mode: 0750
+  when: not ansible_os_family in ["CoreOS", "Container Linux by CoreOS"]