Setting optimization options after initial optimization

[dhblum]

This issue is to address the raising of an error when optimization options try to be changed after an initial optimization is solved. That is in something like the following:

# Instantiate optimization problem
opt_problem = optimization.Optimization(model, \
                                        optimization.EnergyMin, \
                                        optimization.JModelica, \
                                        'q_flow');
# Solve optimization problem                     
opt_problem.optimize(start_time, final_time);
# Get options
opt_options = opt_problem.get_optimization_options();
# Set new options
opt_options['IPOPT_options']['max_iter'] = 2;
opt_options['n_e'] = 2;
opt_options['result_mode'] = 'mesh_points';
opt_problem.set_optimization_options(opt_options)
# Resolve optimization problem                     
opt_problem.optimize(start_time, final_time);

It will raise the following error:

Traceback (most recent call last):
  File "/home/dhb-lx/git/mpcpy/MPCPy/unittests/test_optimization.py", line 261, in test_set_options_iterative
    opt_problem.set_optimization_options(opt_options)
  File "/home/dhb-lx/git/mpcpy/MPCPy/mpcpy/optimization.py", line 177, in set_optimization_options
    return self._package_type._set_optimization_options(opt_options);
  File "/home/dhb-lx/git/mpcpy/MPCPy/mpcpy/optimization.py", line 835, in _set_optimization_options
    raise KeyError('Key {} is set automatically upon solve.'.format(key));
KeyError: 'Key external_data is set automatically upon solve.'