Implement AlwaysCreateOutput for PackParticlesAndVertices

• AlwaysCreateOutput property was defined but never used within the code
• Add a new property AlwaysCreateContainers, which lists the output locations that are to be created regardless of the existence of the input
• There are two instances where this property is set
  • in the stripping it's set to False, and nothing changes
  • in tesla it's set to True, which will cause a warning to be emitted (saying that AlwaysCreateContainers is empty).
• Triggered by LBHLT-134