testprogs: Make testit_expect_failure() return 0 on success

testprogs: Make testit_expect_failure() return 0 on success

This is the behaviour that most existing callers expect, but the
function actually returns a non-zero status code in that case.

Adjust all callers expecting the opposite behaviour to match.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>