Implements ProcessMonitor to watch over external processes

This class takes care of all the spawned external processes,
taking the administrator configured action in the case of any
of the external processes die unexpectedly.

Implements: blueprint agent-child-processes-status

Change-Id: I6bc7a415dde5723dac07589859796c2ffeef5b54
Merge "Implements ProcessMonitor to watch over external processes"