Ubuntu 16.04 OpenVPN
To get the VPN connection to show up in Network Manager, ensure that all these packages are installed:
network-manager-openvpn
network-manager-openvpn-gnome
network-manager-pptp
network-manager-vpnc
It may be overkill but it works.
Even with this, it worked a little flakey on 16.04. One of my PCs threw an error when I tried to open the .ovpn file. I had to configure it manually. On a different PC it worked OK.