Fixup capture/tip/power_rpc27 so that capture returns a positive

ack/nak for a connection so that the connecting process knows what the
hell is going on. Turned out to be necessary for power control since
we do that in parallel, and because it stays busy for 10 seconds on
each power control. I think we will end up revisiting this at some
point, adding blocking connections instead of connect/fail status.