DAOS-18949 container: Fix sched_seq assert failures

[liw]

The assertion "sched_seq1 != sched_seq2" in cont_child_create_start has been triggered likely by the following scenario:

cont_child_create_start
  cont_child_start (the one near the beginning)
    if cont_child->sc_destroy
      returned -DER_CONT_NONEXIST
  vos_cont_create: -DER_EXIST
  assertion failed due to no schduling

This patch changes cont_child_start and ds_cont_child_lookup to return -DER_CONT_DESTROYING instead of -DER_CONT_NONEXIST, so that the scenario above won't reach the vos_cont_create call.

Features: container

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 'erasurecode/multiple_rank_failure.py:EcodOnlineMultiRankFail.test_ec_multiple_rank_failure - timeout destroying container in tearDown'
Status is 'In Progress'
Labels: 'ci_master_weekly,weekly_test'
https://daosio.atlassian.net/browse/DAOS-18949

[liw]

First NLT, then NTL memcheck broke; adding Allow-unstable-test: true.

[daosbuild3]

Test stage Unit Test bdev completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos/job/PR-18269/3/display/redirect

[daosbuild3]

Test stage Test RPMs on EL 9.6 completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18269/4/execution/node/857/log

[liw]

Now Fault Injection and Test RPM failures, sigh; rebasing.

[liw]

Requesting reviews early, since after 4 builds still 0 CI coverage.

[wangshilong]

Thanks for fixing this.

[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-18269/5/execution/node/1384/log

[liw]

Build 5

• [Features: container] container/boundary: DAOS-18610 (timed out, but without the sched_seq assertion failures)

[liw]

Also triggered erasurecode/multiple_rank_failure on top of current pull request (equivalent to build 5): https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos/job/PR-18324/2/artifact/Functional%20Hardware%20Large%20MD%20on%20SSD/erasurecode/multiple_rank_failure.py/. All 3 repeats passed without the sched_req assertion failure.

[liw]

Please see my last two comments on the latest round of testing. Thanks.