Fix propagation of LDB errors through TDB.

Fix propagation of LDB errors through TDB.

Returning a non-zero value from a tdb_traverse callback indicates that tdb_traverse
should stop traversing the database. This error code IS NOT propagated back to the
caller, so LTDB must record the error otherwise. This patch corrects LTDB for this
misunderstanding.

Naturally exposing these errors changes the behaviour of some tests. This commit fixes
that as well.

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