This patch introduces an optional backend encryption for Horizon and
Placement services. When used in conjunction with enabling TLS for
service API endpoints, network communcation will be encrypted end to
end, from client through HAProxy to the Horizon and Placement services.

Change-Id: I9cb274141c95aea20e733baa623da071b30acf2d
Partially-Implements: blueprint add-ssl-internal-network