Drop private argument for include/import role

Since ansible 2.8 dropped private argument is not supported anymore:
https://github.com/ansible/ansible/issues/45038

Change-Id: Iade01544654937a28a606cf2f8900f6fe1587dcb

tasks/main.yml

@@ -100,7 +100,6 @@
 - name: Run the systemd service role
   include_role:
     name: systemd_service
-    private: true
   vars:
     systemd_user_name: "{{ cloudkitty_system_user_name }}"
     systemd_group_name: "{{ cloudkitty_system_group_name }}"