Add ub communicator initialization to validation step

[github-actions]

What does this PR do ?

Fix TP-comm overlap with userbuffer, where validation step precedes a training step.

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[github-actions]

This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days.

[ericharper]

@erhoo82 could you help resolve the conflicts?

[ericharper]

LGTM. Thanks!