Update all Ambari agents

Remove existing certificates from each host and point each agent to the new Ambari server host.

1. On each agent host, stop the agent.
   ambari-agent stop
2. Remove any existing agent certificates.
   rm /var/lib/ambari-agent/keys/*
3. Using a text editor, edit /etc/ambari-agent/conf/ambari-agent.ini to point to the new host.

   [server]
   hostname={NEW_AMBARI_SERVER_FQDN}
   url_port=8440
   secured_url_port=8441