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: I35ba5a711725e65e3d67782b0b29cd678cc43d49

tasks/main.yml

@@ -103,7 +103,6 @@
 - name: Run the systemd service role
   include_role:
     name: systemd_service
-    private: true
   vars:
     systemd_user_name: "{{ swift_system_user_name }}"
     systemd_group_name: "{{ swift_system_group_name }}"