qa: sleep briefly after resetting kclient

Continuation of 6b83f43.

Fixes: https://tracker.ceph.com/issues/40999
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit 602e5f6)

qa/tasks/cephfs/test_client_recovery.py

@@ -227,6 +227,9 @@ def test_stale_caps(self):
         # Simulate client death
         self.mount_a.kill()
 
+        # wait for it to die so it doesn't voluntarily release buffer cap
+        time.sleep(5)
+
         try:
             # Now, after session_timeout seconds, the waiter should
             # complete their operation when the MDS marks the holder's