Fix PyROS Variable Default Initialization

[shermanjasonaf]

Summary/Motivation:

PyROS does not gracefully handle models with:

• uninitialized variables on which the objective function is contingent
• uninitialized second stage variables

as auxiliary variables are initialized to values using the value() method. In either case, an exception is raised by the value() method.

Changes proposed in this PR:

• add exception=False option to the value() method calls used for initializing epigraph and decision rule variables. Consequently, by default, auxiliary variables are not initialized if any of the variables used to
  initialize the auxiliary variables are not initialized.
• add a corresponding unit test

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[jsiirola]

This looks good.

[codecov]

Codecov Report

Merging #2331 (1ef049d) into main (94d1184) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2331      +/-   ##
==========================================
+ Coverage   85.25%   85.33%   +0.07%     
==========================================
  Files         619      619              
  Lines       76425    77923    +1498     
==========================================
+ Hits        65157    66493    +1336     
- Misses      11268    11430     +162     

Flag	Coverage Δ
linux	82.42% <75.00%> (+0.33%)	⬆️
osx	72.66% <75.00%> (+0.18%)	⬆️
other	82.37% <75.00%> (+0.35%)	⬆️
win	79.47% <75.00%> (+0.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pyomo/contrib/pyros/pyros_algorithm_methods.py	88.34% <100.00%> (ø)
pyomo/contrib/pyros/util.py	82.36% <100.00%> (-0.07%)	⬇️
...rmest/examples/reactor_design/leaveNout_example.py	75.00% <0.00%> (-22.50%)	⬇️
pyomo/contrib/pynumero/sparse/mpi_block_matrix.py	57.24% <0.00%> (-9.53%)	⬇️
pyomo/core/kernel/dict_container.py	98.86% <0.00%> (-1.14%)	⬇️
pyomo/solvers/plugins/solvers/gurobi_direct.py	71.91% <0.00%> (-0.51%)	⬇️
examples/pyomobook/test_book_examples.py	96.80% <0.00%> (-0.41%)	⬇️
pyomo/core/kernel/block.py	99.70% <0.00%> (-0.30%)	⬇️
...ocessing/plugins/deactivate_trivial_constraints.py	93.05% <0.00%> (-0.28%)	⬇️
pyomo/core/base/external.py	98.49% <0.00%> (-0.08%)	⬇️
... and 12 more

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