release-24.3: roachtest: deflake c2c/disconnect

[msbutler]

Backport 1/1 commits from #154866 on behalf of @msbutler.

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Previously, the c2c/disconnect roachtest was disconnecting two source nodes, instead of a pair of source/destination nodes. This patch fixes this bug.

Informs: #152248
Informs: #150474

Release note: none

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

✅ PR #155009 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The pull request addresses changes in a non-production file, specifically within the pkg/cmd/roachtest/ directory, which is explicitly listed as pertaining to development tools and test infrastructure. As per the backport policy, changes that affect only non-production code or tests are exempt from the standard backport policy requirements. Therefore, there is no requirement for this PR to justify a critical bug or to utilize a feature flag. Additionally, the PR does not introduce backward-incompatible changes and does not fall under the criteria of requiring feature-flag gating or further justification for a non-critical bug fix.

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[cockroach-teamcity]

This change is