Convert EndpointMap to not require per-service VIP parameters

Convert EndpointMap to not require per-service VIP parameters

Currently we have a hard-coded set of per-service parameters, which
will cause problems for custom roles and full composability.

As a first step towards making this more configurable, remove the
hard-coded per-service parameters from overcloud.yaml, and adjust
the EndpointMap generation to instead accept two mappings, the
ServiceNetMap and a mapping of networks to IPs (effectively this
just moves the map lookup inside the endpoint map instead of
inside overcloud.yaml)

Change-Id: Ib522e89c36eed2115a6586dd5a6770907d9b33db
Partially-Implements: blueprint custom-roles