GetNodeDaemonPort is used to lookup the node daemon port in the services
file, and if not found to return the default one. We make it a generic
function, which accepts the daemon name in input, so that it can be used
by confd as well, to lookup its own udp port.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>