LXC add driver config file lxc.conf

LXC add driver config file lxc.conf

* src/lxc/lxc.conf: new configuration file, there is currently one
  tunable "log_with_libvirtd" that controls whether an lxc controller will
  log only to the container log file, or whether it will honor libvirtd's
  log output configuration. This provides a way to have libvirtd and its
  children log to a single file.  The default is to log to the container
  log file.
* src/Makefile.am libvirt.spec.in: add the new file
* src/lxc/lxc_conf.[ch] src/lxc/lxc_driver.c: read the new log value
  from the configuration file and pass the log informations when
  starting up a container.