Bugs in post-processing of a multi-node CFE run

[amanmajid]

In a multi-node CFE run:

• The C&I capacity plot is not fetching data correctly. We can run the three-node MYS system to reproduce this and put a C&I load on MYSPE.
• The results for 90% and 100% CFE look identical with the above setup.

[amanmajid]

The reason why the 90% and 100% CFE results were the same is because the N_CFE100 run is infeasible. In this case, the workflow saves the outputs from last feasible solution (in this case, N_CFE90). I've now changed this so that results are saved only when we get an optimal result.

[amanmajid]

Issue #7 was closed and merged into this issue.

Issue #7 description: the plot produced showing system unit costs ($/MWh) in the post-processing pipeline is wrong. Oil seems to be plotted even when it isn't in the generation mix.