MDL-37998 quiz settings: disableif rules should accoutn for overrides.

Some form fields are disabled if only one attempt is allowed. However,
there may be an override allowing some students more attempts. We need
to account for that possiblity when setting up the disabled if rules.

Note the disabledIf is good for usability on this complex form, which is
why I don't just want to get rid of them.