Remove ansible<2.2 apt cache hack

Now ansible apt module correctly behaves, so it's time
to deprecate these cruft tasks for apt.

Change-Id: I9d0072bcea8d4cb0c20ded693a0e00177767ee9d

tasks/magnum_install_apt.yml

@@ -13,23 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-#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
-
-- name: Update apt if needed
-  apt:
-    update_cache: yes
-  when: "ansible_date_time.epoch|float - apt_cache_stat.stat.mtime > {{cache_timeout}}"
-
 - name: Install apt packages for Magnum
   apt:
     pkg: "{{ item }}"
     state: "{{ magnum_package_state }}"
+    update_cache: yes
+    cache_valid_time: "{{ cache_timeout }}"
   register: install_magnum_distro_packages
   until: install_magnum_distro_packages |success
   retries: 5