Starting a container with insufficient privilege (correctly) fails
during lxc_init.  However, if starting a daemonized container, we
daemonize before we get to that check.  Therefore while the
container will fail to start, and the logfile will show this, the
'lxc-start -n x -d' command will return success.  For ease of
scripting, do a check for the required privilege before we exit.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>