Fix bug in objective function causing misaligned units_on_cost (#1229)

* Fix bug in objective function causing misaligned units_on_cost
* Sort MPS files before comparing

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Co-authored-by: Abel Soares Siqueira <abel.siqueira@esciencecenter.nl>
Co-authored-by: Diego Alejandro Tejada Arango <diego.tejadaarango@tno.nl>

Author: 3 people