Fix id_to_dn for creating objects

Only do the lookup if the scope is not ONELEVEL
For ONELEVEL, there is no point in paying the price of the lookup.

If the object is not found for scoped queries, return the top level
DN so the object can be created.

Bug 1131265

Change-Id: I1ca41bf87c3bdea30fbdf607b19192f37dd0bfd6