check_cpu.py - usage and IO Wait

This plugin will generate an alert if
* The overall CPU usage exceeds a given threshold
* The overall CPU IO Wait exceeds a given threshold
* The CPU usage of any single CPU core exceeds a threshold
* The CPU IO Wait of any single CPU core exceeds a threshold
* The CPU steal of any single CPU core exceeds a threshold

This plugin also generates performance data suitable for PNP4Nagios, and a suitable PNP4Nagios template is supplied.
The template provides a neater presentation than the default.

Note that this plugin measures CPU usage by reading /proc/stat twice over a time interval (default is 1 second).
As such:
* It is specific to Linux, and probably won't work on other systems
* It does NOT rely on the python library psutil, and hence is backwards compatible
with older Linux systems which do have the psutil library.

New features for version 1.5
* Can alert on overall IO Wait (missing from previous versions)
* Can output the raw values from /proc/stat - see option '-a'
* Also outputs ctxt and processes (context switches and new processes) as performance data (no alerting, just for graphing)

This plugin is a fork of check_cpu.py by Kirk Hammond, and was written to cater for older Linux distributions which do
not have a the library psutil available. It also adds the feature of monitoring IO Wait explicitly.