chroot_execvp()
  Execute an external command (or start an daemon).
  
  This service can be used to start external daemons used by sagator.
  
  Usage: chroot_execvp('daemon_name',args=[],pid_file='')
  
  Where: daemon_name is a string, which defines command name
         args are strings, which defines command line arguments
         pid_file is an string to filename with PID of started daemon
         pgrp_file is an string to a process group filename
  
  Example: chroot_execvp('/usr/sbin/clamd','-c','/etc/clamav.conf')
  
  New in version 0.7.0.