DAOS-16662 test: update some tests to use unique dfuse mount

[daltonbohning]

Update some tests to use unique dfuse mount directory by letting the framework generate one.

Remove mount_dir from run_ior_multiple_variants since it is no longer needed and this level of fine control should be handled per test ideally.

Test-tag: BasicCheckout BasicCheckoutDm DfuseMUPerms IorSmall PosixSimul
Skip-unit-tests: true
Skip-fault-injection-test: true

Required-githooks: true

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[github-actions]

Ticket title is 'Update ior/small.py to use a unique dfuse mount dir'
Status is 'In Progress'
https://daosio.atlassian.net/browse/DAOS-16662

[daosbuild1]

Test stage Functional Hardware Medium Verbs Provider completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-15242/3/execution/node/1072/log

[phender]

FYI the https://build.hpdd.intel.com/job/daos-stack/job/daos/job/PR-15242/3/testReport/junit/FTEST_launch/launch-functional_hardware_medium_verbs_provider/Test_Hardware___Functional_Hardware_Medium_Verbs_Provider___00___launch_py/ error is due to https://daosio.atlassian.net/browse/DAOS-16808

[daltonbohning]

FYI the https://build.hpdd.intel.com/job/daos-stack/job/daos/job/PR-15242/3/testReport/junit/FTEST_launch/launch-functional_hardware_medium_verbs_provider/Test_Hardware___Functional_Hardware_Medium_Verbs_Provider___00___launch_py/ error is due to https://daosio.atlassian.net/browse/DAOS-16808

Thanks. Luckily I don't actually need that stage to run and we have to force land anyway.