Modifying the phase_failures set

For the paint application, we want to add the following failure states for the AGITATE phase:

• Blender inlet valve (from either the base tank or color tank) is open.
• Agitator is stopped (after starting).
• Blender outlet is not closed.

Of course, there could be a number of additional conditions that we would want to add to the list of possible failures, but these will serve to illustrate the concept.