In the black-and-red text box, it appears that Splunk is not running on the cluster master. I would start Splunk and try again.
Once you have Splunk running on the cluster master, the server.conf files that you show should work IF
->test-splunk-master-node-ae26196d0 is a valid server in DNS
->port 8089 is open between the server and the cluster master
Of course this is a test environment, but BTW, the minimum configuration for a multi-site cluster is: one cluster master and 2 sites, where each site has two indexers and a search head.