config+test: use default port for RPC server if one isn't specified

This commit alters the configuration parsing a bit along with the
documentation to expect the RPCHost configuration paramter to also have
the target port specified. If the port isn’t included, then the default
btcd RPC port for that chain is used.

Additionally, within the integration testing framework, when creating
the lnd nodes, we now use the configuration from the btcd harness to
set the proper RPC host.

lnd.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"strings"
 
 	"golang.org/x/net/context"
 
@@ -90,13 +91,16 @@ func lndMain() error {
 		}
 	}
 
-	rpcIP, err := net.LookupHost(cfg.RPCHost)
-	if err != nil {
-		fmt.Printf("unable to resolve rpc host: %v", err)
-		return err
+	// If the specified host for the btcd RPC server already has a port
+	// specified, then we use that directly. Otherwise, we assume the
+	// default port according to the selected chain parameters.
+	var btcdHost string
+	if strings.Contains(cfg.RPCHost, ":") {
+		btcdHost = cfg.RPCHost
+	} else {
+		btcdHost = fmt.Sprintf("%v:%v", cfg.RPCHost, activeNetParams.rpcPort)
 	}
 
-	btcdHost := fmt.Sprintf("%v:%v", cfg.RPCHost, activeNetParams.rpcPort)
 	btcdUser := cfg.RPCUser
 	btcdPass := cfg.RPCPass
 
@@ -120,7 +124,7 @@ func lndMain() error {
 	walletConfig := &btcwallet.Config{
 		PrivatePass: []byte("hello"),
 		DataDir:     filepath.Join(cfg.DataDir, "lnwallet"),
-		RpcHost:     fmt.Sprintf("%v:%v", rpcIP[0], activeNetParams.rpcPort),
+		RpcHost:     btcdHost,
 		RpcUser:     cfg.RPCUser,
 		RpcPass:     cfg.RPCPass,
 		CACert:      rpcCert,