qa/suites/rados/thrash-old-clients: switch to cls/test_cls_rbd.sh workunit

For consistency with other upgrade jobs, don't invoke ceph_test_cls_rbd
directly.  While at it, drop a long outdated filter.

Signed-off-by: Ilya Dryomov <[email protected]>

Author: idryomov

qa/suites/rados/thrash-old-clients/workloads/rbd_cls.yaml

@@ -2,6 +2,7 @@ meta:
 - desc: |
    rbd object class functional tests
 tasks:
-- exec:
-    client.2:
-      - ceph_test_cls_rbd --gtest_filter=-TestClsRbd.get_features:TestClsRbd.parents:TestClsRbd.mirror
+- workunit:
+    clients:
+      client.2:
+        - cls/test_cls_rbd.sh