Map Horizon, Redis, Rabbit, memcached to isolated nets

Map Horizon, Redis, Rabbit, memcached to isolated nets

This change adds parameters to select the networks for Horizon,
Redis, Rabbit MQ, and memcached services. Horizon is often used for
administration from outside the cloud, so if the external network
exists, Horizon will bind to that IP, otherwise it will default to
the Undercloud 'ctlplane' network. Redis, Rabbit MQ, and memcached
will bind to IPs on the internal_api network if it exists, else
they will default to the 'ctlplane' network as well. Any of these
network assignments can be overridden with an environment file.

Change-Id: Ie0aa46b4a3c00d3826866796b4ec3b14f71f987c