test: Avoid redundant stop and error spam on shutdown

Trying to shut down a node after a test failure may fail and lead to an
RPC error.

Also, it is confusing to sidestep the existing fallback to kill any
leftover nodes on a test failure.

So just rely on the fallback.

Idea by Hodlinator.

Co-Authored-By: Hodlinator <172445034+hodlinator@users.noreply.github.com>

Author: MarcoFalke

test/functional/test_framework/test_framework.py

@@ -323,9 +323,12 @@ def shutdown(self):
 
         self.log.debug('Closing down network thread')
         self.network_thread.close()
-        self.log.info("Stopping nodes")
-        if self.nodes:
-            self.stop_nodes()
+        if self.success == TestStatus.FAILED:
+            self.log.info("Not stopping nodes as test failed. The dangling processes will be cleaned up later.")
+        else:
+            self.log.info("Stopping nodes")
+            if self.nodes:
+                self.stop_nodes()
 
         should_clean_up = (
             not self.options.nocleanup and