add tool to gather cpu utilization of threads

* wrap CPU interface
* add cpu_monitor interface
* add test client using cpu_monitor interface
* support for FOC and NOVA

Issue #813
foc: add support to get cpu idle times of kernel

Issue #813
nova: add support to get cpu idle times of kernel

Issue #813
cpu_monitor: provide cpu idle times

works for foc and nova

Fixes #813
cpu_monitor: don't show too bogus values in test
cpu_monitor: show name of task in cpu_monitor test
cpu_monitor: show thread utilization