fix logic for execute log file

fix logic for execute log file

The problem here is that lxc-init runs *inside* the container. So if a
person has the log file set to /home/$USER/foo, lxc-init ends up making a
directory /home/$USER/foo inside the container to put the log file in. What
we really want are the logs to be propagated from inside the container to
the outside. We accomplish this by passing an fd without O_CLOEXEC, and
telling lxc-init to log to that file.

Signed-off-by: Tycho Andersen <tycho@tycho.ws>