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_force_close_test.go

@@ -771,7 +771,7 @@ func testFailingChannel(ht *lntest.HarnessTest) {
 	// totally unrelated preimage.
 	carol := ht.NewNode("Carol", []string{"--hodl.bogus-settle"})
 
-	alice := ht.Alice
+	alice := ht.NewNodeWithCoins("Alice", nil)
 	ht.ConnectNodes(alice, carol)
 
 	// Let Alice connect and open a channel to Carol,