itest: remove the use of standby nodes

This commit removes the usage of the standby nodes and uses
`CreateSimpleNetwork` when applicable. Also introduces a helper method
`NewNodeWithCoins` to quickly start a node with funds.

itest/lnd_channel_backup_test.go

@@ -844,7 +844,7 @@ func runChanRestoreScenarioForceClose(ht *lntest.HarnessTest, zeroConf bool) {
 // and the on-disk channel.backup are updated each time a channel is
 // opened/closed.
 func testChannelBackupUpdates(ht *lntest.HarnessTest) {
-	alice := ht.Alice
+	alice := ht.NewNodeWithCoins("Alice", nil)
 
 	// First, we'll make a temp directory that we'll use to store our
 	// backup file, so we can check in on it during the test easily.
@@ -1052,7 +1052,7 @@ func testExportChannelBackup(ht *lntest.HarnessTest) {
 
 	// With Carol up, we'll now connect her to Alice, and open a channel
 	// between them.
-	alice := ht.Alice
+	alice := ht.NewNodeWithCoins("Alice", nil)
 	ht.ConnectNodes(carol, alice)
 
 	// Next, we'll open two channels between Alice and Carol back to back.