Merge #16115: On bitcoind startup, write config args to debug.log

b951b0973c on startup, write config options to debug.log (Larry Ruane)

Pull request description:

  When a developer is examining `debug.log` after something goes wrong, it's often useful to know the exact options the failing instance of `bitcoind` was started with. Sometimes the `debug.log` file is all that's available for the analysis. This PR logs the `bitcoin.conf` entries and command-line arguments to `debug.log` on startup.

ACKs for top commit:
  MarcoFalke:
    ACK b951b0973c 🐪
  jonatack:
    ACK b951b0973c reviewed diff, re-code review, built, ran tests, launched bitcoind and reviewed debug log output, verified value of  `str` debug log in the added unit test.

Tree-SHA512: bbca4fb3d49f99261758302bde0b8b67300ccc72e7380b01f1f66a146ae8a008a045df0ca5ca9664caff034d0ee38ea7ef38a50f38374525608c07ba52790358

test/functional/test_framework/test_node.py

@@ -298,7 +298,9 @@ class TestNode():
         wait_until(self.is_node_stopped, timeout=timeout)
 
     @contextlib.contextmanager
-    def assert_debug_log(self, expected_msgs, timeout=2):
+    def assert_debug_log(self, expected_msgs, unexpected_msgs=None, timeout=2):
+        if unexpected_msgs is None:
+            unexpected_msgs = []
         time_end = time.time() + timeout
         debug_log = os.path.join(self.datadir, self.chain, 'debug.log')
         with open(debug_log, encoding='utf-8') as dl:
@@ -313,6 +315,9 @@ class TestNode():
                 dl.seek(prev_size)
                 log = dl.read()
             print_log = " - " + "\n - ".join(log.splitlines())
+            for unexpected_msg in unexpected_msgs:
+                if re.search(re.escape(unexpected_msg), log, flags=re.MULTILINE):
+                    self._raise_assertion_error('Unexpected message "{}" partially matches log:\n\n{}\n\n'.format(unexpected_msg, print_log))
             for expected_msg in expected_msgs:
                 if re.search(re.escape(expected_msg), log, flags=re.MULTILINE) is None:
                     found = False