Currently, hbal exits with status 1 if early exit is requested, even
when all jobs are successful. This is counter-intuitive behaviour, so
let's fix it (Issue 386).

Note that the man page had conflicting information already, so it's a
good thing to clean this up.

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