DAOS-16495 test: Use the test env control config file w/ dmg (#15094)

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Use the TestEnvironment.conftrol.config file by default with the DmgCommand object when a config file is not specified.

Skip-unit-tests: true
Skip-fault-injection-test: true
Test-tag: DmgNvmeScanTest ConfigGenerateOutput ConfigGenerateRun HarnessConfigTest

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[github-actions]

Ticket title is 'Several control/config_generate_output.py tests fail on weekly testing stating localhost with connection refused error.'
Status is 'Awaiting backport'
Labels: '2.6.1rc1,ci_master_weekly,weekly_test'
https://daosio.atlassian.net/browse/DAOS-16495

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All tests passed in https://build.hpdd.intel.com/job/daos-stack/job/daos/job/PR-15149/2/testReport/