Merge bitcoin/bitcoin#31620: test: Remove --noshutdown flag, Tidy startup failures

faf2f2c654 test: Avoid redundant stop and error spam on shutdown (MarcoFalke)
fae3bf6b87 test: Avoid redundant stop and error spam on startup failure (MarcoFalke)
fa0dc09b90 test: Remove --noshutdown flag (MarcoFalke)
fad441fba0 test: Treat leftover process as error (MarcoFalke)

Pull request description:

  The `--noshutdown` flag is brittle, confusing, and redundant:

  * Someone wanting to inspect the state after a test failure will likely also want to debug the state on the python side, so the option is redundant with `--pdbonfailure`. If there was a use case to replicate `--pdbonfailure` without starting pdb, a dedicated flag could be added for that use case.
  * It is brittle to use the flag for a passing test, because it will disable checks in the test. For example, on shutdown LSan will perform a leak check, and the test framework will check that the node did not crash, and it will check that the node did not print errors to stderr.

  Fix all issues by removing it.

  Also, tidy up startup error messages to be less confusing as a result.

ACKs for top commit:
  hodlinator:
    re-ACK faf2f2c654
  pablomartin4btc:
    re tACK faf2f2c654

Tree-SHA512: 46d7ae59c7be88b93f1f9e0b6be21af0fc101e646512e2c5e725682cb18bfec8aa010e0ebe89ce9ffe239e5caac0da5f81cc97b79e738d26ca5fa31930e8e4e3

test/functional/test_framework/test_node.py

@@ -20,6 +20,7 @@ import time
 import urllib.parse
 import collections
 import shlex
+import sys
 from pathlib import Path
 
 from .authproxy import (
@@ -158,7 +159,6 @@ class TestNode():
         self.rpc = None
         self.url = None
         self.log = logging.getLogger('TestFramework.node%d' % i)
-        self.cleanup_on_exit = True # Whether to kill the node when this object goes away
         # Cache perf subprocesses here by their data output filename.
         self.perf_subprocesses = {}
 
@@ -200,11 +200,11 @@ class TestNode():
     def __del__(self):
         # Ensure that we don't leave any bitcoind processes lying around after
         # the test ends
-        if self.process and self.cleanup_on_exit:
+        if self.process:
             # Should only happen on test failure
             # Avoid using logger, as that may have already been shutdown when
             # this destructor is called.
-            print(self._node_msg("Cleaning up leftover process"))
+            print(self._node_msg("Cleaning up leftover process"), file=sys.stderr)
             self.process.kill()
 
     def __getattr__(self, name):