DAOS-18799 pool: Fix handle loading

[liw]

It appears that if the PS leader skips the ds_pool_iv_conn_hdls_update
call during pool_svc_step_up_cb because there's no pool handle in the
DB, IV fetches for pool handles will create invalid IV entries and
return unexpected -DER_NOTLEADERs. To prevent that, this patch changes
pool_svc_step_up_cb to call ds_pool_iv_conn_hdls_update even if there's
no pool handle in the DB.

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 'Infinite DER_NOTLEADER loop on single-server DAOS cluster after pool create'
Status is 'In Progress'
https://daosio.atlassian.net/browse/DAOS-18799

[daosbuild3]

Test stage NLT completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos/job/PR-18016/1/display/redirect

[daosbuild3]

Test stage Unit Test completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos/job/PR-18016/1/display/redirect

[liw]

Mark as ready for reviews, for the CI testing is too slow at the moment.

[daosbuild3]

Test stage Functional Hardware Medium MD on SSD completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18016/2/testReport/

[liw]

Build 2:

• dfuse/daos_build: SRE-3745

[wangshilong]

A bit tricky, but looks workable. So if ->iv_valid is true it means IV is updated. but It could be empty/dummy value.

[wangshilong]

Probably should go 2.8 as well, NOT leader errors are confusing and annoying