Don't call it an error if a container exits without calling sys_reboot.
Particularly since that will almost always be the case with lxc-execute.
This fixes a regression introduced in commit
"49296e2ebfe7c5f9d6ebafbb54f5c5e56a0cc085: support proper container
reboot"
Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>