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: I74205322b1e2c7951d69222e22c3f6913b6d73d5

defaults/main.yml

@@ -13,6 +13,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+## APT Cache Options
+cache_timeout: 600
+
 # Default galera connection address
 galera_address: 127.0.0.1
 galera_root_user: root

tasks/galera_client_install.yml

@@ -13,14 +13,22 @@
 # 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:
+    - galera-client-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}}" or
+    add_repo | changed
   tags:
     - galera-client-apt-packages