Test flake chase (Apr 8, 2026) (backport #15967) (backport #15968)

[mergify]

1. Give peer-started nodes more than 15s to boot to reduce the probability of CI flakes
2. Fix a test that assumes that random bytes would never return a valid Erlang term prefix. Yes, it actually happened
3. Adopt await_condition/2 in several CLI tests that used timer:sleep/1

References #15222.

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This is an automatic backport of pull request #15967 done by Mergify.

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This is an automatic backport of pull request #15968 done by Mergify.

[mergify]

Cherry-pick of d0204ef has failed:

On branch mergify/bp/v4.2.x/pr-15968
Your branch is up to date with 'origin/v4.2.x'.

You are currently cherry-picking commit d0204ef89f.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   deps/rabbit/test/feature_flags_v2_SUITE.erl
	modified:   deps/rabbit/test/rabbit_stream_sac_coordinator_SUITE.erl

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   deps/rabbitmq_ct_helpers/src/rabbit_ct_broker_helpers.erl

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[michaelklishin]

Doh #15966