Add 'lxc.logfile' and 'lxc.loglevel' config items.  Values provided on
the command line override the config items.

Have lxccontainer not set a default loglevel and logfile.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>