Support multiple 'execute_on' with UOs, PPS, and VectorPPS
refs #3446
Merge pull request #3601 from permcody/shared_ptr_pps

Support multiple 'execute_on' with UOs, PPS, and VectorPPS
Merge commit '7e0a256603c7b8edcc8f04c7f81aac3b82d86f13'