pre-provisioned nodes hostnames should not resolve to 127.0.0.1

[James Slagle]

We need to document that when setting up pre-provisioned nodes for use with deployed-server-environment.yaml, the nodes need to have resolvable externally routable hostnames and not resolve to 127.0.0.1.

If the hostnames resolve to 127.0.0.1, the pacemaker cluster will never form since pacemaker will only be listening on 127.0.0.1.

See https://access.redhat.com/discussions/2745661 for more details.

This includes the Undercloud itself as well. Otherwise when installing with undercloud_public_host set to the hostname, if that hostname resolves to 127.0.0.1, then all Undercloud services will only be bound to 127.0.0.1/loopback.

Note that the most likely cause here is users explicitly adding a line like:

127.0.0.1 <hostname>

to /etc/hosts

or appending <hostname> to the existing 127.0.0.1.

We should explicitly say not to do this when using pre-provisioned nodes for both the undercloud and overcloud nodes.