libs/utils/env.py: Add gem5 support
Created by: valschneider
Gem5 is now a board option for TestEnv configuration. board_settings is used to define the simulation
Results directory was being initialized after reading the configurations and setting up the targets. This initialization has been moved up in the code so that is it made before reading the configurations, the result path is thus now available for the initialization of certain boards (e.g. gem5)