release-24.1: 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 #155008 does not comply with backport policy

Confidence: high
Explanation: The PR aims to backport a change for the 'c2c/disconnect' roachtest, located within the designated non-production directory 'pkg/cmd/roachtest/'. Although changes in this path are usually treated as non-production and thus exempt from standard backport policies, the PR description does not contain a 'Release justification: .*' line with a valid justification. Additionally, the commit does not fix a critical bug outlined by the specified critical bug criteria nor does it introduce a feature gated by a default-disabled feature flag. The changes seem to address an issue with the test mechanics rather than the database system's stability, security, data handling, or performance.
Recommendation: Reconsider the backport or provide a valid release justification explicit in the PR description.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[jeffswenson]

LGTM

[github-actions]

Reminder: it has been 3 weeks please merge or close your backport!