Reduce the amount of Process information retrieved in the auto-locker

When looking for opened files, the current code does:

# function: get_open_files() from autolock.py
for proc in psutil.process_iter():
    ....

This returns a lot of unused informations and we are seeing several memory errors in that function. As we just need the PID, we could lower the amount of data retrieved using:

for proc in psutil.process_iter(attrs=["pid"]):
    ....