DAOS-18236 test: run daos_racer/parallel with mpich

[daltonbohning]

Run daos_racer/parallel with mpich instead of openmpi.
Also verify MPI is found when running.

Test-tag: DaosRacerParallelTest
Skip-unit-tests: true
Skip-fault-injection-test: true

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 'daos_racer/parallel.py:DaosRacerParallelTest.test_daos_racer_parallel - Failed to initialize step=2, rc=-1025'
Status is 'In Progress'
Labels: '2.6.4-aurora.p1,2.8.0tb1,ci_master_provider,ci_master_weekly,daily_test,request_for_2.6.5,testp1,weekly_test'
Job should run at elevated priority (1)
https://daosio.atlassian.net/browse/DAOS-18236