Only update apt cache if necessary

Workarounding the upstream ansible apt module bug
documented here:
https://github.com/ansible/ansible-modules-core/pull/1517

For the next versions of ansible we'll be using, we should
check if the apt bug is fixed. When it's fixed, we could
abandon this change and use the standard apt module
with correct cache handling.

Change-Id: I2aaf00da175f31d0157bbc4ae30a4e176b055078

defaults/main.yml

@@ -17,6 +17,9 @@
 debug: False
 verbose: True
 
+## APT Cache options
+cache_timeout: 600
+
 # Name of the virtual env to deploy into
 keystone_venv_tag: untagged
 keystone_venv_bin: "/openstack/venvs/keystone-{{ keystone_venv_tag }}/bin"

tasks/keystone_install.yml

@@ -13,14 +13,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- name: Update apt sources
+#TODO(evrardjp): Replace the next 2 tasks by a standard apt with cache
+#when https://github.com/ansible/ansible-modules-core/pull/1517 is merged
+#in 1.9.x or we move to 2.0 (if tested working)
+- name: Check apt last update file
+  stat:
+    path: /var/cache/apt
+  register: apt_cache_stat
+  tags:
+    - keystone-apt-packages
+
+- name: Update apt if needed
   apt:
     update_cache: yes
-    cache_valid_time: 600
-  register: apt_update
-  until: apt_update|success
-  retries: 5
-  delay: 2
+  when: "ansible_date_time.epoch|float - apt_cache_stat.stat.mtime > {{cache_timeout}}"
   tags:
     - keystone-apt-packages