qa/cephfs: use different config options to generate MDS_TRIM

qa/cephfs: use different config options to generate MDS_TRIM

Test test_with_health_warn_trim in classes TestFSFail and TestMDSFail
use config options mds_log_trim_decay_rate and mds_log_trim_threshold
to generte health warning MDS_TRIM which is required for this test.

Since these config options are not present in Reef, use config options
mds_log_max_segments and mds_log_warn_factor to generate health
MDS_TRIM.

Fixes: https://tracker.ceph.com/issues/66829
Signed-off-by: Rishabh Dave <ridave@redhat.com>