Setting up RHDS with a CNAME DNS alias for the General.FullMachineName fails because the IP address does not reverse-resolve back to the hostname provided

Issue

• We have a DNS alias for an original server, which we want to use as the name for our directory server.

• We have done this with RHDS8 and RHDS9:

  # host cname
  cname.example.com is an alias for hostname.example.com
  hostname.example.com address 192.168.1.21
  # host 192.168.1.21
  21.1.168.192.in-addr.arpa domain name pointer hostname.example.com.
  

• However, with the current setup-ds-admin.pl for RHDS10 (and now also for RHDS9), setup fails with the following message:

  [15/10/20:11:08:53] - [Setup] Info Creating directory server . . .
  [15/10/20:11:08:53] - [Setup] Info Hostname 'cname.example.com' is valid, but none of the IP addresses resolve back to cname.example.com
  [15/10/20:11:08:53] - [Setup] Info - address 192.168.1.21 resolves to host hostname.example.com
  [15/10/20:11:08:53] - [Setup] Fatal Error: Could not create directory server instance 'instance'.
  [15/10/20:11:08:53] - [Setup] Fatal Exiting . . .
  

• This wasn't the case with RHDS8 and probably earlier versions of RHDS9, we managed to install fine with just a server CNAME alias in DNS.

• Vanilla install of RHDS 10 using setup-ds-admin.pl, but using the [3] Custom option and setting the machine name to the alias instead of the hostname.
• This occurs always, both on current RHDS10 install and RHDS9 install with latest software updates. We need this fixed at least for RHDS10.