Remove extra keystone admin haproxy listen and allow TLS

Remove extra keystone admin haproxy listen and allow TLS

The current code exposes an unused public listen directive in HAProxy
for the keystone admin endpoint. This is not ideal and should be
removed, as it exposes the service unnecessarily. We should stick to
just exposing it to the ctlplane network as is the default.

If folks really need to expose it to the public network, they can do so
by modifying the ServiceNetMap through t-h-t and setting the keystone
admin endpoint's network to external.

Now, for "single" or "internal" haproxy endpoints, this adds the ability
to detect if they're using the external network, and thus use TLS on it.
Which is something a deployer would want if they exposed the keystone
admin endpoint in such a way.

Change-Id: I79563f62fd49a4f7654779157ebda3c239d6dd22
Closes-Bug: #1710909
Closes-Bug: #1639996