Don't pass negative descriptor to install_service_fd

CID 996213 (#1 of 1): Improper use of negative value (NEGATIVE_RETURNS)
7. negative_returns: "new_logfd" is passed to a parameter that cannot be negative.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>