ldb_tdb: Prepare to handle rename with GUID index by using ltdb_search_base()

ldb_tdb: Prepare to handle rename with GUID index by using ltdb_search_base()

This will allow use of a GUID TDB key in the future.  While ltdb_search_base()
might be marginally slower than tdb_exists(), no allocation is done for the
attributes or DN, and renmaes are not a very common operation.

This allows a check if the target DN exists even when the direct DN -> key
link is broken.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>