Reporting Solver Failure

[bknueven]

1. What Pyomo return codes to check (our approach, Egret's approach, check_optimal_termination)
2. What to do on error (mostly raise an Exception, not in xhatters, not at Iter0)
3. two solve_ones: ‎mpisppy/utils/xhat_eval.py‎ & ‎mpisppy/spopt.py; consider consolidating