Remove epel-6 repo
yum remove epel-release
Enable epel-7 repo:
wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
rpm -ivh epel-release-latest-7.noarch.rpm
Or
wget https://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-9.noarch.rpm
rpm -ivh epel-release-7-9.noarch.rpm
edit the /etc/yum.repos.d/epel.repo file and make sure you have enabled=1
or run yum-config-manager --enable epel
then install openvpn:
yum update
yum install openvpn easy-rsa