DAOS-19028 test: REBUILD29 use more precise timing (#18546)

[kccain]

Before this change, rebuild_kill_PS_leader_during_rebuild() killed a non-leader engine and immediately (tried to) inject fault DAOS_REBUILD_TGT_SCAN_HANG on "all engines". This fault injection itself suffered RPC timeouts due to the killed engine. This further affected the test's overall timing, contradicting the goal of killing the PS leader engine during the first rebuild.

With this change, the test no longer uses fault injection. Instead it waits for the first rebuild to start and demonstrate evidence of scanning activity (rs_toberb_obj_nr > 0). This is accomplished using a new common function test_rebuild_wait_to_scanning_next() that waits for both the rs_version (pool map version) to increment and the to-be-rebuilt number of objects to become nonzero.

Test-repeat: 10
Test-tag: test_rebuild_29
Skip-unit-tests: true
Skip-fault-injection-test: true
Skip-test-rpms: true

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/rebuild.py:DaosCoreTestRebuild.test_rebuild_29 - pool reintegrate failed'
Status is 'In Progress'
Labels: '2.6.5rc3,pr_test,request_for_2.8,scrubbed_2.8,tcp_provider,test_2.6.5rc1'
https://daosio.atlassian.net/browse/DAOS-19028

[daosbuild3]

Test stage Functional on EL 9 completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18630/1/execution/node/847/log

[daosbuild3]

Test stage Functional on EL 9 completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18630/2/execution/node/847/log

[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-18630/2/execution/node/1016/log

[daosbuild3]

Test stage Functional Hardware Medium Verbs 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-18630/2/execution/node/1161/log

[kccain]

Test-tag testing passed https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos/job/PR-18630/2/testReport/FTEST_daos_test/

Other stage failures are another issue in which no test tags were found to run in those cluster environments. Filed an SRE issue for this. https://daosio.atlassian.net/browse/SRE-3898

Ready for review.