chroot_execvpe()
  Execute an external command (or start an daemon) and update variables.
  
  This service can be used to start external daemons used by sagator.
  You also can set environment varibles.
  
  Usage: chroot_execvpe('daemon_name',args=[],env={})
  
  Where: daemon_name is a string, which defines command name
         args are strings, which defines command line arguments
         env is an dictionary of environment variables
         pid_file is an string to filename with PID of started daemon
         pgrp_file is an string to a process group filename
  
  Example: chroot_execvpe('/usr/sbin/clamd',['-c','/etc/clamav.conf'],
                          {'LANG': 'C'})
  
  New in version 0.7.0.