Add a sleep() prior to calling tasks to ensure postop writes are done

We were seeing a rare deadlock of DS when creating the memberOf task because
one thread was adding memberOf in a postop while another was trying to
create an index and this was causing a PRLock deadlock.

ipaserver/install/ldapupdate.py

@@ -265,6 +265,9 @@ class LDAPUpdate:
     def create_index_task(self, attribute):
         """Create a task to update an index for an attribute"""
 
+        # Sleep a bit to ensure previous operations are complete
+        time.sleep(5)
+
         r = random.SystemRandom()
 
         # Refresh the time to make uniqueness more probable. Add on some