cloudinfo: identify gce from file

utils/cloudinfo/gce.go

@@ -15,15 +15,27 @@
 package cloudinfo
 
 import (
+	"io/ioutil"
 	"strings"
 
 	info "github.com/google/cadvisor/info/v1"
 
+	"github.com/golang/glog"
 	"google.golang.org/cloud/compute/metadata"
 )
 
+const (
+	gceProductName = "/sys/class/dmi/id/product_name"
+	google         = "Google"
+)
+
 func onGCE() bool {
-	return metadata.OnGCE()
+	data, err := ioutil.ReadFile(gceProductName)
+	if err != nil {
+		glog.V(2).Infof("Error while reading product_name: %v", err)
+		return false
+	}
+	return strings.Contains(string(data), google)
 }
 
 func getGceInstanceType() info.InstanceType {