We see the error as conflict between packages:
file /usr/lib/python2.6/site-packages from install of ambari-agent-126.96.36.199-143.x86_64 conflicts with file from package ambari-server-188.8.131.52-0.x86_64
This error indicates that you have AmbariServer package of version 184.108.40.206.0 but trying to install Ambari-Agent of version 220.127.116.11-143 (slightly higher). Which is causing the conflict.
Please check if you have duplicate ambari repos like (18.104.22.168-143 as well as 22.214.171.124.0 both) on the same host?
In that case remove the Old unwanted ambari repo from the mentioned dir and then perform a yum clean.
# grep baseurl /etc/yum.repos.d/* | grep ambari
So can you please try this:
# yum clean all
Then retry the agent installation or try the "yum upgrade ambari-server" first and then upgrade the agent.
# sudo yum upgrade ambari-server
# sudo yum upgrade ambari-agent