DAOS-18976 rebuild: bump rebuild gen when leader retry the rebuild

[liuxuezhao]

If on the same PS leader, it retry the rebuild/reclaim on same version, should bump the generation.

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 'Aurora rebuild failing with DER_HG / DER_SHUTDOWN'
Status is 'In Progress'
Labels: 'test_2.6.5rc1'
https://daosio.atlassian.net/browse/DAOS-18976

[wangshilong]

So this pr #18289 is not needed? bump new gen means it won't return EBUSY and will abort previous last rebuild scan

[liuxuezhao]

So this pr #18289 is not needed? bump new gen means it won't return EBUSY and will abort previous last rebuild scan

I think PR18289 still needed. It make SCAN exit earlier when finalize, and the race for rebuild_pool_tls_lookup() still need to fix even if abort the old gen rebuild.