Fix panic when meminfo couldn't be read

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
(cherry picked from commit 5f7b1b604c)
Signed-off-by: Tibor Vass <tibor@docker.com>

daemon/info.go

@@ -51,6 +51,7 @@ func (daemon *Daemon) SystemInfo() (*types.Info, error) {
 	meminfo, err := system.ReadMemInfo()
 	if err != nil {
 		logrus.Errorf("Could not read system memory info: %v", err)
+		meminfo = &system.MemInfo{}
 	}
 
 	sysInfo := sysinfo.New(true)