autopilot/interface+choice: add NodeScore type

We create a new type NodeScore which is a tuple (NodeID, score). The
weightedChoice and chooseN algorithms are altered to expect this type.

This is done in order to simplify the types we are using, since we were
only using a subset of the fields in AttachmentDirective.

autopilot/agent.go

@@ -571,22 +571,43 @@ func (a *Agent) openChans(availableFunds btcutil.Amount, numChans uint32,
 		return fmt.Errorf("unable to calculate node scores : %v", err)
 	}
 
-	// Add addresses to the candidates.
-	for nID, c := range scores {
-		addrs := addresses[nID]
-		c.Addrs = addrs
-	}
-
 	log.Debugf("Got scores for %d nodes", len(scores))
 
-	// Now use the score to make a weighted choice which
-	// nodes to attempt to open channels to.
-	chanCandidates, err := chooseN(numChans, scores)
+	// Temporary convert to NodeScore.
+	nodeScores := make(map[NodeID]*NodeScore)
+	for k, v := range scores {
+		nodeScores[k] = &NodeScore{
+			NodeID: v.NodeID,
+			Score:  v.Score,
+		}
+	}
+
+	// Now use the score to make a weighted choice which nodes to attempt
+	// to open channels to.
+	nodeScores, err = chooseN(numChans, nodeScores)
 	if err != nil {
 		return fmt.Errorf("Unable to make weighted choice: %v",
 			err)
 	}
 
+	chanCandidates := make(map[NodeID]*AttachmentDirective)
+	for nID := range nodeScores {
+		// Add addresses to the candidates.
+		addrs := addresses[nID]
+
+		// If the node has no known addresses, we cannot connect to it,
+		// so we'll skip it.
+		if len(addrs) == 0 {
+			continue
+		}
+
+		chanCandidates[nID] = &AttachmentDirective{
+			NodeID:  nID,
+			ChanAmt: chanSize,
+			Addrs:   addrs,
+		}
+	}
+
 	if len(chanCandidates) == 0 {
 		log.Infof("No eligible candidates to connect to")
 		return nil