test: signal the process for exit before shutting down local goroutines

This commit is tied to the prior commit and it patches up a lingering
race condition and deadlock that can arise due to now properly waiting
for all goroutine  to exit before concluding the shutdown process.

lnd_test.go

@@ -1509,6 +1509,7 @@ func testRevokedCloseRetribution(net *networkHarness, t *harnessTest) {
 
 	// Next query for Bob's channel state, as we sent 3 payments of 10k
 	// satoshis each, Bob should now see his balance as being 30k satoshis.
+	time.Sleep(time.Millisecond * 200)
 	bobChan, err := getBobChanInfo()
 	if err != nil {
 		t.Fatalf("unable to get bob's channel info: %v", err)

networktest.go

@@ -279,12 +279,17 @@ func (l *lightningNode) Stop() error {
 	default:
 	}
 
+	if runtime.GOOS == "windows" {
+		if err := l.cmd.Process.Signal(os.Kill); err != nil {
+			return err
+		}
+	} else if err := l.cmd.Process.Signal(os.Interrupt); err != nil {
+		return err
+	}
+
 	close(l.quit)
 	l.wg.Wait()
-	if runtime.GOOS == "windows" {
-		return l.cmd.Process.Signal(os.Kill)
-	}
-	return l.cmd.Process.Signal(os.Interrupt)
+	return nil
 }
 
 // Restart attempts to restart a lightning node by shutting it down cleanly,