lntest: more descriptive errors for CloseChannel

This improves the error reporting for the harness' CloseChannel so that
the exact step where closure fails can be better indicated.

This is to help debug some flaky failures in the CI.

lntest/harness.go

@@ -1128,7 +1128,8 @@ func (n *NetworkHarness) CloseChannel(ctx context.Context,
 		// within the network.
 		closeResp, err := closeRespStream.Recv()
 		if err != nil {
-			errChan <- err
+			errChan <- fmt.Errorf("unable to recv() from close "+
+				"stream: %v", err)
 			return
 		}
 		pendingClose, ok := closeResp.Update.(*lnrpc.CloseStatusUpdate_ClosePending)
@@ -1140,11 +1141,13 @@ func (n *NetworkHarness) CloseChannel(ctx context.Context,
 
 		closeTxid, err := chainhash.NewHash(pendingClose.ClosePending.Txid)
 		if err != nil {
-			errChan <- err
+			errChan <- fmt.Errorf("unable to decode closeTxid: "+
+				"%v", err)
 			return
 		}
 		if err := n.WaitForTxBroadcast(ctx, *closeTxid); err != nil {
-			errChan <- err
+			errChan <- fmt.Errorf("error while waiting for "+
+				"broadcast tx: %v", err)
 			return
 		}
 		fin <- closeTxid
@@ -1153,9 +1156,6 @@ func (n *NetworkHarness) CloseChannel(ctx context.Context,
 	// Wait until either the deadline for the context expires, an error
 	// occurs, or the channel close update is received.
 	select {
-	case <-ctx.Done():
-		return nil, nil, fmt.Errorf("timeout reached before channel close " +
-			"initiated")
 	case err := <-errChan:
 		return nil, nil, err
 	case closeTxid := <-fin: