Lower the CPU usage (especially on singe core machine)

[mastrolinux]

In single-core machines, when running apt-get list as a subprocess, we end up in using the whole CPU.
This is visible, especially on old Raspberry-Pi and BeagleBone.
Please enable changing the priority of the process. I think running as root automatically has more priority. On single-core computers, the priority should be lower than other processes.