hspace and hbal treat -O differently, and use aliases for short names
(although hbal succeeds in that, and hspace doesn't). Uniform this with
a name lookup, using the same functions we used for instance
selection/exclusion.

Some of the code is by the way a bit repetitive, and could probably be
merged in a single function. That needs to be a monadic one, though, so
I promise to do it as soon as I realize how to write them! ;)

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>