Merge bitcoin/bitcoin#28253: test: display abrupt shutdown errors in console output

0f83ab407e test: display abrupt shutdown errors in console output (furszy)

Pull request description:

  Making it easier to debug errors in the CI environment,
  particularly in scenarios where it's not immediately clear
  what happened nor which node crashed (or shutdown abruptly).

  A bit of context:
  Currently, the test framework redirects each node's stderr output
  stream to a different temporary file inside each node's data directory.
  While this is sufficient for storing the error, it isn't very helpful for
  understanding what happened just by reading the CI console output.

  Most of the time, reading the stderr file in the CI environment is not
  possible, because people don't have access to it.

  Testing Note:
  The displayed error difference can be observed by cherry-picking this
  commit 9cc5393c0f on top of this branch and running any
  functional test.

ACKs for top commit:
  maflcko:
    lgtm ACK 0f83ab407e
  theStack:
    ACK 0f83ab407e

Tree-SHA512: 83ce4d21d5316e8cb16a17d3fbe77b8649fced9e09410861d9674c233f6e9c34bcf573504e387e4f439c2841b2ee9855d0d35607fa13aa89eafe0080c45ee82d

test/functional/test_framework/test_node.py

@@ -234,8 +234,13 @@ class TestNode():
         poll_per_s = 4
         for _ in range(poll_per_s * self.rpc_timeout):
             if self.process.poll() is not None:
+                # Attach abrupt shutdown error/s to the exception message
+                self.stderr.seek(0)
+                str_error = ''.join(line.decode('utf-8') for line in self.stderr)
+                str_error += "************************\n" if str_error else ''
+
                 raise FailedToStartError(self._node_msg(
-                    'bitcoind exited with status {} during initialization'.format(self.process.returncode)))
+                    f'bitcoind exited with status {self.process.returncode} during initialization. {str_error}'))
             try:
                 rpc = get_rpc_proxy(
                     rpc_url(self.datadir, self.index, self.chain, self.rpchost),