test: Fix intermittent issue in p2p_segwit.py #21792

Calling start_node might call wait_for_rpc_connection, which will fail.

https://cirrus-ci.com/task/5669555591708672?logs=ci#L3504

  File "/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/test/functional/p2p_segwit.py", line 1974, in test_upgrade_after_activation
    self.start_node(2, extra_args=["-reindex", f"-segwitheight={SEGWIT_HEIGHT}"])
  File "/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/test/functional/test_framework/test_framework.py", line 508, in start_node
    node.wait_for_rpc_connection()
  File "/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/test/functional/test_framework/test_node.py", line 224, in wait_for_rpc_connection
    raise FailedToStartError(self._node_msg(
test_framework.test_node.FailedToStartError: [node 2] bitcoind exited with status 1 during initialization

Actually I have no idea how this test could even pass in the first place. All code paths here should eventually raise FailedToStartError, which shouldn't be caught and thus fail the test.

If someone wants to investigate this, that'd be great. Though the diff here should still be correct, as assert_start_raises_init_error is the proper way to check for init errors.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #20799 (net processing: Only support version 2 compact blocks by jnewbery)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Maybe rebase in light of #21804 merge.

Rebased, as requested by @Sjors

ACK fad6269916dbf8adc14d757a18f19c74e95cf659

ACK fad6269

Thank for the fix, and showing me assert_start_raises_init_error @MarcoFalke. I am incorporating this into #21090 as well. It is indeed perplexing that the error was only intermittent.

Verifying the efficacy of this patch.

• The 4 days before this PR was merged there were 235 builds of master on cirrusCI resulting in 4 p2p_segwit.py failures.
• Since its merge, there have been 343 builds of master and 0 p2p_segwit.py failures.