connman: Include vpn-script in FILES

When vpnc support is included through PACKAGECONFIG, there
is now an extra vpn-script coming after the atest upgrade,
include that script into FILES so it gets packaged.

Signed-off-by: Alejandro Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>