log: Don't override -v0 with -v2

If we specify log level to none (0) the result is LOG_INFO (2).

Acked-by: Andrew Vagin <avagin@parallels.com>
Acked-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>