vzctl start: close extra FDs later

Close extra FDs just before executing /sbin/init. This way we will
be able to show errors from exec_container_init().

https://bugzilla.openvz.org/3091

Reported by Sergey Korshunov <seyko2@gmail.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
vzctl start: mkdir /proc in CT if needed

Although this is a rare case, there might be a container with
/proc directory missing. As we already take care of mounting it,
why not also create it (ignoring the fact that it already exists,
but reporting any other error).

This makes it possible to start CT if there's no /proc inside it.

https://bugzilla.openvz.org/3091

Reported-by: Sergey Korshunov <seyko2@gmail.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>