Define and bind a public virtual IP

Prior to this change our heat templates define one virtual IP, which all
the services are bound to.

We wish to be able to segregate these endpoints: some need to be
accessible to "the public"; some are only intended to be accessed within
the cloud; some are only for admin use.

This change adds a second VIP which we can use for binding only the
endpoints that are intended to be publicly accessible, leaving the older
VIP to be used for internal end points.

Haproxy is told to also listen on that new VIP so that we can expose selected
services via the new VIP, and keepalived is in charge of assigning the VIP to
control plane nodes.

This change has a proposed split of services between control-only and
control+public interfaces. Assuming our yaml parsers (in merge.py and
Heat) understand YAML anchors/aliases, and assuming I've got the syntax
right, this should get expanded so that all the control+public services
get their config defined from the same block without needing to repeat
it for each service. (AFAICT both merge.py and heat use pyyaml, which
does support aliases/anchors)

The default is left at binding to only the controlplane interface, so
that new services added to this map will default to being internal-only

This patchset partially completes a spec which will one day live at
https://blueprints.launchpad.net/tripleo/+specs/tripleo-juno-virtual-public-ips
but for now can bee seen in  Id9addc65f0d2ed519ce4b3edbd561ed660a2786e

Implements: blueprint tripleo-juno-virtual-public-ips
Change-Id: I9649ee74ebaf62b6b929b28243a07c789a08867c
Co-Authored-By: Robert Collins <rbtcollins@hp.com>
Partial-Bug #1325114
Merge "Define and bind a public virtual IP"