DAOS-15992 client: set st_blksize in ostatx_cb() and add unit test

[wiliamhuang]

Python buffered read/write relies on st_blksize as default buffer size. dfuse calls dfs_ostatx() which returns stat with zero st_blksize. Consequently, 4096 for st_blksize is returned to application.

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[github-actions[bot]]

Ticket title is 'st_blksize in stat is not set inside ostatx_cb' Status is 'Awaiting backport' Labels: 'scrubbed_2.8' Job should run at elevated priority (1) https://daosio.atlassian.net/browse/DAOS-15992

[daosbuild1]

Test stage Functional Hardware Medium completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-14666/2/execution/node/1563/log

[daosbuild1]

Test stage Functional Hardware Medium UCX Provider completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-14666/2/execution/node/1709/log

[wiliamhuang]

The failures in hardware tests in CI are not related to this PR. Existing tickets, https://daosio.atlassian.net/browse/DAOS-15608 https://daosio.atlassian.net/browse/DAOS-16168 https://daosio.atlassian.net/browse/DAOS-15243

[mchaarawi]

could you please rebase with latest 2.6 and push again? thanks

[wiliamhuang]

could you please rebase with latest 2.6 and push again? thanks

Thank you! I just merged this PR with release/2.6.

[daosbuild1]

Test stage Functional Hardware Medium completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-14666/4/execution/node/1508/log

[wiliamhuang]

The only failure is an existing issue. https://daosio.atlassian.net/browse/DAOS-16315 dfuse/pil4dfs_fio.py:Pil4dfsFio.test_pil4dfs_vs_dfs - test timeout running fio