add a timeout in case a system-container refuses to quit

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>

config/types.go

@@ -130,6 +130,7 @@ type RancherConfig struct {
 	ResizeDevice        string                                    `yaml:"resize_device,omitempty"`
 	Sysctl              map[string]string                         `yaml:"sysctl,omitempty"`
 	RestartServices     []string                                  `yaml:"restart_services,omitempty"`
+	ShutdownTimeout     int                                       `yaml:"shutdown_timeout,omitempty"`
 }
 
 type UpgradeConfig struct {