DAOS-18078 test: Fix pool/rf.py

[phender]

Remove the system_ram_reserved server config setting to make use of the default. This should avoid the Available memory (RAM) insufficient error being seen with this test. Also update the server storage and pool size settings to allow the test to be used to verify MD on SSD configurtations.

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 'pool/rf.py:PoolRedunFacProperty.test_rf_pool_property - Available memory (RAM) insufficient for configured 168 GiB ram-disk size'
Status is 'Open'
Labels: '2.8.0tb1,ci_master_weekly,weekly_test'
https://daosio.atlassian.net/browse/DAOS-18078