On a Fedora or CentOS system with enables selinux you need to store your certificate and configuration in /etc/openvpn to avoid selinux is blocking the access of NetworkManager to this files. There is a way of setting some sebooleans to allow selinux to read them from user home directories but for me it didn't work and I did not investigate. I moved all files on that machine to /etc/openvpn and modified the NetworkManager configuration. Everything works like a charm now. And it is quite more comfortable to configure all the details like if you wish to route all your traffic through that vpn connection or not.