test: make assertNumOpenChannelsPending poll every 200ms

In this commit, we modify the assertNumOpenChannelsPending to poll
every 200ms rather than just a single attempt. The goal of this commit
is to reduce the number of flakes on travis caused by slow instances.

lnd_test.go

@@ -245,6 +245,13 @@ func numOpenChannelsPending(ctxt context.Context, node *lightningNode) (int, err
 // number of pending channels between them.
 func assertNumOpenChannelsPending(ctxt context.Context, t *harnessTest,
 	alice, bob *lightningNode, expected int) {
+
+	const nPolls = 10
+
+	ticker := time.NewTicker(200 * time.Millisecond)
+	defer ticker.Stop()
+
+	for i := 0; i < nPolls; i++ {
 		aliceNumChans, err := numOpenChannelsPending(ctxt, alice)
 		if err != nil {
 			t.Fatalf("error fetching alice's node (%v) pending channels %v",
@@ -255,15 +262,28 @@ func assertNumOpenChannelsPending(ctxt context.Context, t *harnessTest,
 			t.Fatalf("error fetching bob's node (%v) pending channels %v",
 				bob.nodeID, err)
 		}
-	if aliceNumChans != expected {
+
+		isLastIteration := i == nPolls-1
+
+		aliceStateCorrect := aliceNumChans == expected
+		if !aliceStateCorrect && isLastIteration {
 			t.Fatalf("number of pending channels for alice incorrect. "+
 				"expected %v, got %v", expected, aliceNumChans)
 		}
-	if bobNumChans != expected {
+
+		bobStateCorrect := bobNumChans == expected
+		if !bobStateCorrect && isLastIteration {
 			t.Fatalf("number of pending channels for bob incorrect. "+
 				"expected %v, got %v",
 				expected, bobNumChans)
 		}
+
+		if aliceStateCorrect && bobStateCorrect {
+			return
+		}
+
+		<-ticker.C
+	}
 }
 
 // assertNumConnections asserts number current connections between two peers.