Do not break if OS variables not found

Allows to run the role on other systems, even if a variables file has
not been defined for it.

Author: aruhier

tasks/variables.yml

@@ -1,7 +1,11 @@
 ---
 # Variable configuration.
 - name: Include OS-specific variables.
-  include_vars: "{{ ansible_os_family }}.yml"
+  include_vars: "{{ item }}"
+  with_first_found:
+    - files:
+      - "vars/{{ ansible_os_family }}.yml"
+      skip: true
   when: ansible_os_family != "RedHat"
 
 - name: Include OS-specific variables (RedHat).