Pyomo.DOE enchancement: add support for stochastic programming decompositions

[adowling2]

Summary

Steps:

1. Mimic parmest to automatically formulate local extensive form using create_ef.py and scenario_tree.py (import from parmest)
2. Verify Pyomo.DOE works with new approach (regression testing)
3. Verify parmest works using mpi-sppy on a handful of examples
4. Verify Pyomo.DOE works using mpi-sppy on a handful of examples
5. Computational timings -- what is the benefit of decompositions
6. Move create_ef.py, scenario_tree.py, and similar supporting files to a utility folder in pyomo? Okay to import from parmest for now (utility folder), revisit with mpi-sppy team later.