reconciler: return all stopped allocs

[chrisroberts]

Description

The AllocReconciler.handleStop function returns an array of stopped
allocations, however it would only return the stopped allocations of
a single task group. This updates it to return all the stopped
allocations and adds a test to verify all expected allocations are
returned when a job has multiple task groups.

Testing & Reproduction steps

Links

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
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Reviewer Checklist

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• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

[tgross]

LGTM!

[tgross]

@chrisroberts this looks like it ends up being a bug, right? Assuming you've observed that, we should get a changelog entry into this PR and get it merged to go out in the upcoming release.