Currently when a run is marked to stop we are going to stop currently running
tasks and then their childs will be marked as skipped.
But tasks not depending on a stopped task (root task or childs with a finished
parent) that are just waiting for an executor slot, will be scheduled when
there will be a free slot also if the run is marked to stop (and then the
scheduler will stop them after some seconds).
This patch will mark all not started tasks as skipped when the run is marked to
stop.