This converts our existing puppeted mailman configuration into a set of
ansible roles and a new playbook. We don't try to do anything new and
instead do our best to map from puppet to ansible as closely as
possible. This helps reduce churn and will help us find problems more
quickly if they happen.
Followups will further cleanup the puppetry.
Change-Id: If8cdb1164c9000438d1977d8965a92ca8eebe4df
4c4e27cb3a