Accounted for multicore machines in CPU usage
Speeded up CPU usage chart drawing.
By default, psutil waits 0.1 seconds per get_cpu_percent() call. This is
very slow for getting the CPU percent of each process on a system. By
calling get_cpu_percent(interval=0) for each process on the system, THEN
waiting to allow psutil to collect CPU time data, THEN calling
get_cpu_percent(interval=0) for each process, we only need to wait once.