narval #2557391 use a WF to manage execution_status [validation pending]

For now, execution status of a Plan is an attribute, it should be a WF (so it is atomic)

prioritynormal
typetask
done in4.0.0
load1.000
load left0.000
closed by#4dc262a514b5 replace Plan.execution_status with a workflow (closes #2557391)
patchreplace Plan.execution_status with a workflow (closes #2557391) [applied]