qa/tasks/ceph: use tell <pgid> deep_scrub in osd_scrub_pgs

This is the more modern variant.  Crimson doesn't currently
support the pg <pgid> deep_scrub variant, so let's just use
this one generally.

Signed-off-by: Samuel Just <sjust@redhat.com>

qa/tasks/ceph.py

@@ -1303,7 +1303,7 @@ def osd_scrub_pgs(ctx, config):
                     # request was missed.  do not do it every time because
                     # the scrub may be in progress or not reported yet and
                     # we will starve progress.
-                    manager.raw_cluster_cmd('pg', 'deep-scrub', pgid)
+                    manager.raw_cluster_cmd('tell', pgid, 'deep_scrub')
             if gap_cnt > retries:
                 raise RuntimeError('Exiting scrub checking -- not all pgs scrubbed.')
         if loop: