Add cron to pull playbooks

TrivialFix

Change-Id: I9e7e65d6e5ddfb3c387e147a8cc6f5aae1aab0cd

ansible/roles/common/tasks/pull.yml

@@ -10,3 +10,9 @@
     action: "pull_image"
     common_options: "{{ docker_common_options }}"
     image: "{{ heka_image_full }}"
+
+- name: Pulling cron image
+  kolla_docker:
+    action: "pull_image"
+    common_options: "{{ docker_common_options }}"
+    image: "{{ cron_image_full }}"