DAOS-19340 test: set FI log level to warn for rebuild tests

[kccain]

Test-tag: test_rebuild_36
Test-repeat: 10
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_36 - timeout waiting for rebuild'
Status is 'Reopened'
Labels: '2.8.0rc2,ci_2.8_weekly,daily_test,verbs_provider'
https://daosio.atlassian.net/browse/DAOS-19340