Don't use node0 as sender of IX transactions

node0 tends to have many small UTXOs which result in TXs with many inputs
and high CPU usage.

qa/rpc-tests/dip3-deterministicmns.py

@@ -365,7 +365,7 @@ def test_instantsend(self, tx_count, repeat, timeout=20):
         for j in range(repeat):
             for i in range(tx_count):
                 while True:
-                    from_node_idx = random.randint(0, len(self.nodes) - 1)
+                    from_node_idx = random.randint(1, len(self.nodes) - 1)
                     from_node = self.nodes[from_node_idx]
                     if from_node is not None:
                         break