switched to using create() if create_instance() is unavailable, to avoid breaking on older pyomo installs
switched to using create() if create_instance() is unavailable, to avoid breaking on older pyomo installs

bmaluenda/SWITCH-Pyomo-Chile,bmaluenda/SWITCH-Pyomo-Chile,OCM-Lab-PUC/switch-chile,bmaluenda/switch,OCM-Lab-PUC/switch-chile