Fixes for RaspberryPi

Handles some process-related fixes for RaspberryPi:

* `SystemInfo#num_processors` - processor is lower-case. Modified the regex. Also, I modified this to return 1 if an error occurs rather than nil as nil breaks things when determining process cpu usage per-processor. 
* Updated the process cpu usage % calculations to return 0 if Infinity or NaN is the calculated value.