DAOS-18888 client: validation check when event completion

[Nasf-Fan]

It is suspected that some event completion callback maybe repeatedly triggered against UCX provider under the cases of network trouble. If that is true, it will misguide the subsequent thread-private event owner.

The patch will check such completion against stale event and skip it.

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is 'daos_test/suite.py:DaosCoreTest.test_daos_single_rdg_tx'
Status is 'In Progress'
Labels: 'pr_test'
https://daosio.atlassian.net/browse/DAOS-18888

[daosbuild3]

Test stage Functional Hardware Large MD on SSD completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18208/2/execution/node/1279/log

[daosbuild3]

Test stage Functional Hardware Medium MD on SSD completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18208/2/execution/node/1228/log

[daosbuild3]

Test stage Functional Hardware Medium UCX Provider MD on SSD completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18208/2/execution/node/1238/log