Description of problem:
When scale up cluster with quick install tool, after input new node info, it require user to re-set cluster hostname.  if user doesn't  give a right cluster hostname , it may be overwriten by an incorrect default value.

  openshift_master_cluster_hostname: x.x.x.x
  openshift_master_cluster_public_hostname: x.x.x.x

Version-Release number of selected component (if applicable):
atomic-openshift-utils-3.4.32-1.git.0.076b279.el7.noarch

How reproducible:
always

Steps to Reproduce:
1.trigger an scale against existed cluster with quick install tool.
2.after input new node info, it will hint user to set cluster hostname as following:
<--snip-->
Do you want to add additional hosts? [y/N]: n

You have chosen to install a single master cluster (non-HA).

In a single master cluster, the cluster host name (Ansible variable openshift_master_cluster_public_hostname) is set by default to the host name of the single master. In a multiple master (HA) cluster, the FQDN of a host must be provided that will be configured as a proxy. This could be either an existing load balancer configured to balance all masters on
port 8443 or a new host that would have HAProxy installed on it.

(Optional)
If you want to override the cluster host name now to something other than the default (the host name of the single master), or if you think you might add masters later to become an HA cluster and want to future proof your cluster host name choice, please provide a FQDN. Otherwise, press ENTER to continue and accept the default.

Enter hostname or IP address [openshift-151.lab.eng.nay.redhat.com]: 

<--snip-->

Actual results:
The original cluster hostname was modified  to incorrect value.

Expected results:
The step to setting cluster hostname in node scale up process is useless.