Fix cov_report directory in sim.py
Fix cov_report directory in sim.py

Enables us to save coverage groups text file which helps easily see the overall
coverage in a regression.

AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex