DAOS-18531 vos: setup ts_set in vos_obj_incarnate()

[NiuYawei]

Replace the vos_obj_hold() call before vos_obj_incarnate() with vos_obj_acquire() to ensure the ts_set setup is fully done within transaction, that can make code cleaner and avoid following race:

• Updater A called vos_obj_hold(), it failed to find the OI and mark the obj entry in ts_set as negative.
• Updater A yield.
• Concurrent updater B created OI and setup obj->obj_df.
• Updater A resumed to call vos_obj_incarnate(), it found that the obj->obj_df is non-NULL so skipped OI creation.
• The ts_set for updater A is now in an inconsistent state, it's negative but without 'se_create_idx' set.

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 'mdonssd phase 2: Assertion 'set_entry->se_create_idx != NULL' failed'
Status is 'In Progress'
Labels: 'md_on_ssd2,request_for_2.6.5,request_for_2.8,test_2.8,testp1'
https://daosio.atlassian.net/browse/DAOS-18531

[daosbuild3]

Test stage NLT completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-17957/1/testReport/