DAOS-16100 test: Fix stopping daos_test during timeout (#15275)

[phender]

Fix stopping timed out processes run by a JobManager class by only searching for and killing the command executable being run by clush, orterun, mpirun, etc. Add a new harness/cmocka.py test to verify the stopping of the processes with a test timeout.

Skip-unit-tests: true
Skip-fault-injection-test: true
Test-tag: pr daos_test dfuse_test test_load_mpi HarnessCmockaTest
Allow-unstable-test: true

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[github-actions]

Ticket title is 'daos_test/suite.py:DaosCoreTest.test_daos_degraded_ec - cart_ctl error due to errored rank 0'
Status is 'Awaiting backport'
Labels: '2.6.0rc1,ci_impact,pr_test,tcp_provider,testp2'
Job should run at elevated priority (1)
https://daosio.atlassian.net/browse/DAOS-16100

[daosbuild1]

Test stage Functional on EL 8.8 completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-15603/1/execution/node/825/log

[phender]

Test stage Functional on EL 8.8 completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-15603/1/execution/node/825/log

The harness/cmocka.py test failures are expected.