DAOS-16969 test: Reduce cleanup operations for metadata.py test (#15779)

[phender]

Remove the calling of cleanup methods for multiple containers and ior commands that can be handled by destroying the pool and a single ior kill command.

Skip-unit-tests: true
Skip-fault-injection-test: true
Skip-func-hw-test-large-md-on-ssd: false
Test-tag: ObjectMetadata

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[github-actions]

Ticket title is 'server/metadata.py:ObjectMetadata.test_metadata_server_restart'
Status is 'Awaiting backport'
Labels: '2.6.3rc1,2.6.3rc2,ci_2.6_weekly,ci_master_weekly,request_for_2.6.3,testp2,weekly_test'
https://daosio.atlassian.net/browse/DAOS-16969