Distributed letsencrypt cert storage

[byrnedo]

Currently, the ingress runs on all nodes, but effectively should only be used on one node, since there's no synchronisation between instances (think TLS certs and data used by letsencrypt).

The auto-ssl library we use supports a redis file store, would be nice to have a play book to configure redis if the user want's ingress via multiple nodes.

Another alternative is a distributed fs. Not a bad option given that it's mostly reads going on.}

Yet another option: implement an s3 driver for auto-ssl: cheap n easy then to configure that.