ovpn: Convert from servername -> server_url

* Previously the server name cached the common name generated during
  init and assumed always 1194/udp.
* The new configuration allows for users to pass in a url in a new form
  that allows the protocol to be specified as well as the port.
* Example: udp://vpn.example.com:1194
* Try to be backwards compatible.
ovpn: Remove reference to udp/1194

* Remove references to udp/1194.
* Works better with non-standard ports and tcp.