Verify lxc cache file after download

This patch adds a sha256sum verification to the lxc cache file
download task and also sets the task to retry.

Change-Id: Ie6342c1ee004a3d2de2256408361259d2fb47f1b
Closes-Bug: #1482091
(cherry picked from commit 0ccf11eeddaad8b8f4b53e3a7cf3f33f81d208ee)

playbooks/inventory/group_vars/hosts.yml

@@ -40,6 +40,7 @@ openstack_upstream_url: "http://{{ openstack_upstream_domain }}"
 lxc_container_caches:
   - url: "{{ openstack_upstream_url }}/container_images/rpc-trusty-container.tgz"
     name: "trusty.tgz"
+    sha256sum: "56c6a6e132ea7d10be2f3e8104f47136ccf408b30e362133f0dc4a0a9adb4d0c"
 
 
 ## RabbitMQ

playbooks/roles/lxc_hosts/defaults/main.yml

@@ -68,3 +68,4 @@ lxc_apt_packages:
 # lxc_container_caches:
 #   - url: "{{ openstack_upstream_url }}/container_images/rpc-trusty-container.tgz"
 #     name: "trusty.tgz"
+#     sha256sum: "56c6a6e132ea7d10be2f3e8104f47136ccf408b30e362133f0dc4a0a9adb4d0c"

playbooks/roles/lxc_hosts/tasks/lxc_cache.yml

@@ -19,7 +19,10 @@
     dest: "/var/cache/lxc_{{ item.name }}"
     mode: "0644"
     force: no
+    sha256sum: "{{ item.sha256sum }}"
   register: cache_download
+  retries: 3
+  delay: 10
   until: cache_download|success
   with_items: lxc_container_caches
   tags: