Use apt_repository update_cache feature

With ansible 2.2, apt_repository update_cache feature has
been fixed. When a new repo will be added, apt-get update
will be run after the addition if update_cache is set to yes.

This combined with the apt module now properly checking the
cache validity, we can now have proper updating of the cache
with registering variables.

Change-Id: Icb10352ef319bfbc80151708393e81e7533a1f13

tasks/galera_client_install_apt.yml

@@ -57,6 +57,7 @@
   apt_repository:
     repo: "{{ galera_client_repo }}"
     state: present
+    update_cache: yes
   register: add_repo
   until: add_repo | success
   retries: 5
@@ -64,13 +65,6 @@
   tags:
     - galera-client-repos
 
-- name: Update apt if needed
-  apt:
-    update_cache: yes
-  when: add_repo | changed
-  tags:
-    - galera-client-apt-packages
-
 - name: Install galera packages
   apt:
     pkg: "{{ item }}"