Add a unexpanded lxc_conf

Add a unexpanded lxc_conf

Currently when a container's configuration file has lxc.includes,
any future write_config() will expand the lxc.includes.  This
affects container clones (and snapshots) as well as users of the
API who make an update and then c.save_config().

To fix this, separately track the expanded and unexpanded lxc_conf.  The
unexpanded conf does not contain values read from lxc.includes.  The
expanded conf does.  Lxc functions mainly need the expanded conf to
figure out how to configure the container.  The unexpanded conf is used
at write_config().

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>