rename physical nics at shutdown

rename physical nics at shutdown

When a physical nic is being set up, store its ifindex and original name
in struct lxc_conf.  At reboot, reset the original name.
We can't just go over the original network list in lxc_conf at shutdown
because that may be tweaked in the meantime through the C api.  The
saved_nics list is only setup during lxc_spawn(), and restored and
freed after lxc_start.

Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1086244

Changelog: remove non-effect change in execute.c

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