[sv-ac] disabling action blocks for vacuous and disabled attempt

Hi,

we have been converging more on the following solution:

The action block should by default execute the action block (as it is
now), but there should be tasks like $assertvacuouson/off,
$assertdisableon/off, $assertfailon/off (or other names that are more
expressive) that then allow truning off or on the execution of the
action block under different conditions.

ed