I dont think changing the host name fixed the problem, but you bypassed the real issue in doing what you did by switching to centos6.local. During the confirm hosts step a python script is called that reads ambari-agent.ini to look up the host name. It seems as if this script or something else appends to the host name the host extension value AGAIN making it impossible to find the host and thus bombing. I was tracing through the install and I found the issue.
What worked for me – Before you run the Ambari installation, check ambari-agent.ini in /etc/ambari-agent.conf you’ll should expect to see a line that matches your HOST (for example):
Mine was incorrectly written-
…so, after I cleaned up the script and re-ran the install I was able to get past the CONFIRM HOSTS step
I am running CentOS 6.5 Ambari 1.5 HD 2.2