Optimise apt cache update task

The update of the apt cache and the package installation
can all be handled in a single task by providing the
package action plugin with the right parameters. This
removes an extra task to optimise execution.

Also, Ansible 2.x allows the package module to consume
the package list in the name parameter instead of using
a with_items loop which further optimises the execution.

The minimum Ansible version is raised to 2.2 due to a
known bug [1] in Ansible's apt module which does not
update the cache properly if the cache update and the
install are combined in a single task.

[1] https://github.com/ansible/ansible-modules-core/issues/1497

Change-Id: Ia15e468a70f1ac90d8b7ce88f930f81e01afa3d4
(cherry picked from commit c35cacbf4c)

meta/main.yml

@@ -18,7 +18,7 @@ galaxy_info:
   description: Installation and setup of horizon
   company: Rackspace
   license: Apache2
-  min_ansible_version: 2.0
+  min_ansible_version: 2.2
   platforms:
     - name: Ubuntu
       versions:

tasks/horizon_install.yml

@@ -13,13 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- name: Ensure apt cache is up to date
-  apt:
-    update_cache: yes
-    cache_valid_time: "{{ cache_timeout }}"
-  when:
-    - ansible_pkg_mgr == 'apt'
-
 - name: Create horizon dir
   file:
     path: "{{ item.path }}"
@@ -46,13 +39,14 @@
 
 - name: Install distro packages
   package:
-    name: "{{ item }}"
+    name: "{{ horizon_distro_packages }}"
     state: "{{ horizon_package_state }}"
+    update_cache: "{{ (ansible_pkg_mgr == 'apt') | ternary('yes', omit) }}"
+    cache_valid_time: "{{ (ansible_pkg_mgr == 'apt') | ternary(cache_timeout, omit) }}"
   register: install_packages
   until: install_packages|success
   retries: 5
   delay: 2
-  with_items: "{{ horizon_distro_packages }}"
 
 - name: Create developer mode constraint file
   copy: