Generate a config file for each client generated

 * Add an openvpn_server variable
 * Move `${openvpn_client}.{key,csr,crt}` to
   `${openvpn_client}/client.{key,csr,crt}`
 * Generate `${openvpn_client}/${openvpn_server}.ovpn` config file
 * Copy over a self contained directory of file per client that can be
   imported by networkmanager in ubuntu or run directly with `sudo
   openvpn ${openvpn_server}.ovpn`