example_test.py: fixup coinbase height argument, derive number clearly

Author: instagibbs

test/functional/example_test.py

@@ -164,13 +164,13 @@ def run_test(self):
         self.tip = int(self.nodes[0].getbestblockhash(), 16)
         self.block_time = self.nodes[0].getblock(self.nodes[0].getbestblockhash())['time'] + 1
 
-        height = 1
+        height = self.nodes[0].getblockcount()
 
         for i in range(10):
             # Use the mininode and blocktools functionality to manually build a block
             # Calling the generate() rpc is easier, but this allows us to exactly
             # control the blocks and transactions.
-            block = create_block(self.tip, create_coinbase(height), self.block_time)
+            block = create_block(self.tip, create_coinbase(height+1), self.block_time)
             block.solve()
             block_message = msg_block(block)
             # Send message is used to send a P2P message to the node over our P2PInterface