DAOS-19246 test: use REBUILD_POOL_SIZE for dfs_extend_write_kill/_extend

[liuxuezhao]

In dfs_extend_write_kill() tests, hits -DER_NOSPACE in extend_cb_internal() -> case EXTEND_UPDATE's extend_write() -> dfs_write() assert_int_equal(rc, 0);
It then cause the test case abort and do cleanup - test_teardown() -> pool_destroy_safe() -> wait_rebuild hang, as in dfs_extend_internal() it set DAOS_REBUILD_TGT_SCAN_HANG but no chance to reset it when hit DER_NOSPACE and abort.

So increase dfs_extend_write_kill/_extend()'s pool size to REBUILD_POOL_SIZE to avoid that case.

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/suite.py:DaosCoreTest.test_daos_extend_simple - Failure assert_rc_equal src/tests/suite/daos_rebuild_common.c:91 DER_MISC(-1025) != DER_SUCCESS(0)'
Status is 'In Review'
Labels: 'ci_master_daily,pr_test'
https://daosio.atlassian.net/browse/DAOS-19246

[wangshilong]

Not related to this PR, just wondering if might be better if we could reset fail_loc inside test_teardown() before pool destroy is called in case similar issues happen in other case?

[liuxuezhao]

Not related to this PR, just wondering if might be better if we could reset fail_loc inside test_teardown() before pool destroy is called in case similar issues happen in other case?

right, I considered like that - add fail_loc_set flag in test_arg_t, set it when set the fail_loc, then in test_teardown() if the flag is not cleared then reset it to 0. In test_arg_t already with fail_loc/_num/_value those used in some test cases but not on some other test cases. And change that will affect many test cases. So I just increase pool size to simplify the change and avoid affect too much tests.