Scripts are executed when external actions required.
CRTOOLS_SCRIPT_ACTION contains a required action.
If a script doesn't know a current action, it should exit with 0.

The first usecase will be lock/unlock network.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>