Fix hydra UID

The style for IDs dictates that groups/users should have the same ID -
so if a user doesn't have a group or vice versa, then we should skip
that ID.

In this case, we had already assigned grsecurity GID 121, but I
accidentally also assigned Hydra UID 121. Instead, let's assign Hydra
UID 122. And also assign a GID (122) as well.

Luckily nobody was depending on this yet (except me).

Signed-off-by: Austin Seipp <aseipp@pobox.com>