Merge OS-specific variables for ubuntu

Now that we are using systemd everywhere, for xenial++ there isn't a
need to release specific settings.

Change-Id: I9fb735e8f7455b7266d90b5275e7d0b90512722a
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

tasks/main.yaml

@@ -13,7 +13,7 @@
 # under the License.
 ---
 - name: Include OS-specific variables.
-  include_vars: "{{ ansible_distribution|lower }}-{{ ansible_distribution_release }}.yaml"
+  include_vars: "{{ ansible_distribution|lower }}.yaml"
   when: ansible_os_family == 'Debian'
 
 - name: Include OS-specific variables.