Unable to install or update using yum
It appears you have a Centos 6 machine but have configured the Epel repository for Centos 7. That is not going to work. Remove it and install the Centos 6 Epel Repository at:
wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
Make sure you uninstall anything you added from the Centos 7 Epel repository as well.
That should do it.
Run the following
yum remove epel-release
Then run yum update
That should fix your problem