pytest:sid_strings: test SIDs as search base

pytest:sid_strings: test SIDs as search base

As a way of testing the interpretation of a SID string in a remote
server, we search on the base DN "<SID=x>" where x is a non-existent
or malformed SID.

On Windows some or all malformed SIDs are detected before the search
begins, resulting in a complaint about DN syntax rather than one about
missing objects.

From this we can get a picture of what Windows considers to be
a proper SID in this context.

Samba does not make a distinction here, always returning NO_SUCH_OBJECT.

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