DAOS-18710 test: Update provider tests to use dc_x for UCX.

[jgmoore-or]

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 'Change to using ucx+dc_x as the provider string for daily test run with UCX and for the weekly provider tests.'
Status is 'Open'
Labels: 'request_for_2.8'
https://daosio.atlassian.net/browse/DAOS-18710

[daosbuild3]

Test stage Functional on Leap 15.6 completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos/job/PR-17746/1/display/redirect