qa/cephfs: add MDS_CLIENTS_BROKEN_ROOTSQUASH to ignorelist
MDS_CLIENTS_BROKEN_ROOTSQUASH is generated and expected by
test_rootsquash_nofeature but it hasn't be added to ignorelist as a
result of which QA code marks the job as failed even though all tests
finished running successfully.
Introduced-by: bccc8ceb471c441ec04d7eb2c353630f8c5ce843 Fixes: https://tracker.ceph.com/issues/66075 Signed-off-by: Rishabh Dave <ridave@redhat.com>