test: Fix race condition in index pruning test

Nodes are restarted and reconnected as part of the test. Afterwards
`sync_blocks` is called immediately on the nodes. `sync_blocks`
first checks that all the included nodes have at least one
connection. Since adding a connection is usually happening in a
thread, sometimes nodes could run into this check before the
connection was fully established so that it would fail the entire
test.

This fix uses the `connect_nodes` helper to make the connection the
nodes. `connect_nodes` has a wait for the connection built into it.

Author: fjahr

test/functional/feature_index_prune.py

@@ -8,7 +8,6 @@
     assert_equal,
     assert_greater_than,
     assert_raises_rpc_error,
-    p2p_port,
 )
 
 
@@ -132,11 +131,11 @@ def run_test(self):
             self.nodes[i].assert_start_raises_init_error(extra_args=self.extra_args[i], expected_msg=msg)
 
         self.log.info("make sure the nodes start again with the indices and an additional -reindex arg")
-        ip_port = "127.0.0.1:" + str(p2p_port(3))
         for i in range(3):
-            # The nodes need to be reconnected to the non-pruning node upon restart, otherwise they will be stuck
-            restart_args = self.extra_args[i]+["-reindex", f"-connect={ip_port}"]
+            restart_args = self.extra_args[i]+["-reindex"]
             self.restart_node(i, extra_args=restart_args)
+            # The nodes need to be reconnected to the non-pruning node upon restart, otherwise they will be stuck
+            self.connect_nodes(i, 3)
 
         self.sync_blocks(timeout=300)