WIP: Run nginx for SSL and load-balancing.

Purpose:
  Enable SSL on all endpoints for security, and
  load-balance all endpoints for availability.

Changes:
  - run nginx on all controller nodes
  - pull ssl cert and key from vars, install to /etc/nginx/ssl
  - configure an 'openstack' nginx site
  - add nginx endpoints to front horizon and all api services

TODO:
  - use upstream { ... } to point each nginx to every
    controller.
  - update keystone service catalog to use new endpoints