qa: Only allow calling TestNode.stop() after connecting

(Still tolerate calling it on a no longer (self.)running node, as in a node that has been queried for is_node_stopped() and modified state before returning True).

Tests should not attempt to use the non-functioning RPC interface to call stop() unless wait_for_connections() has succeeded.

No longer log and suppress http.client.CannotSendRequest as a consequence of stop()-RPC, as error conditions causing this knock-on issue are now guarded against before the call.

test/functional/test_framework/test_node.py

@@ -8,7 +8,6 @@ import contextlib
 import decimal
 import errno
 from enum import Enum
-import http.client
 import json
 import logging
 import os
@@ -307,10 +306,11 @@ class TestNode():
                     # overhead is trivial, and the added guarantees are worth
                     # the minimal performance cost.
                 self.log.debug("RPC successfully started")
+                # Set rpc_connected even if we are in use_cli mode so that we know we can call self.stop() if needed.
+                self.rpc_connected = True
                 if self.use_cli:
                     return
                 self.rpc = rpc
-                self.rpc_connected = True
                 self.url = self.rpc.rpc_url
                 return
             except JSONRPCException as e:
@@ -396,15 +396,15 @@ class TestNode():
         """Stop the node."""
         if not self.running:
             return
+        assert self.rpc_connected, self._node_msg(
+            "Should only call stop_node() on a running node after wait_for_rpc_connection() succeeded. "
+            f"Did you forget to call the latter after start()? Not connected to process: {self.process.pid}")
         self.log.debug("Stopping node")
-        try:
         # Do not use wait argument when testing older nodes, e.g. in wallet_backwards_compatibility.py
         if self.version_is_at_least(180000):
             self.stop(wait=wait)
         else:
             self.stop()
-        except http.client.CannotSendRequest:
-            self.log.exception("Unable to stop node.")
 
         # If there are any running perf processes, stop them.
         for profile_name in tuple(self.perf_subprocesses.keys()):