Use existing roles DRY out playbook - certificates

[brucellino]

There are several tasks in the playbook which have been re-implemented here although they are provided by existing roles. I suggest this playbook re-uses roles which are already published, in order to reduce the size of the playbook and improve maintainability. See #7 for context

As a suggested first stab at this, the IGTF playbook could be replaced with AAROC.certificates with needs_cert=false or something.