Resolve file path with {{ role_path }}

I was getting errors with this playbook when executing "include OS
family/distribution specific variables." Even though my
`ansible_os_family` is `RedHat`, `with_first_found` was finding no
results. (I am running Centos 7, but I confirmed the `RedHat` value
in the ansible facts with `ansible all -m setup`.)

When I prepended the `defaults/...` relative path with `{{ role_path
}}`, this playbook ran successfully.

Author: Jon Wolski

tasks/main.yml

@@ -12,8 +12,8 @@
 - name: include OS family/distribution specific variables
   include_vars: "{{ item }}"
   with_first_found:
-    - "defaults/{{ ansible_os_family | lower }}-{{ ansible_distribution | lower }}.yml"
-    - "defaults/{{ ansible_os_family | lower }}.yml"
+    - "{{ role_path }}/defaults/{{ ansible_os_family | lower }}-{{ ansible_distribution | lower }}.yml"
+    - "{{ role_path }}/defaults/{{ ansible_os_family | lower }}.yml"
   tags: installation
 
 - include: debug.yml