ldb:pyldb exposes Result type

ldb:pyldb exposes Result type

You perhaps never want to manually create results (as in `x = Result()`)
-- except maybe in tests -- and that would be why we never added it in
the first place (or rather, we never noticed that it ws missing).

But we do want to sometimes go `isinstance(x, ldb.Result)`, and that
is how we noticed it was missing now.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>