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: I9ae5bde63f2f2356b310e2b2d4f042cb250d13df

tasks/manila_install.yml

@@ -57,7 +57,6 @@
 - name: Run the systemd service role
   include_role:
     name: systemd_service
-    private: true
   vars:
     systemd_user_name: "{{ manila_system_user_name }}"
     systemd_group_name: "{{ manila_system_group_name }}"