update vendored go-checkpoint

vendor/github.com/weaveworks/go-checkpoint/checkpoint.go

@@ -118,18 +118,19 @@ func Check(p *CheckParams) (*CheckResponse, error) {
 		p.OS = runtime.GOOS
 	}
 
-	// If we're not given a Signature, then attempt to read one.
-	signature := p.Signature
-	if p.Signature == "" {
-		var err error
-		if p.SignatureFile == "" {
-			signature, err = getSystemUUID()
-		} else {
-			signature, err = checkSignature(p.SignatureFile)
-		}
-		if err != nil {
-			return nil, err
-		}
+	// If we're not given a Signature, then attempt to read one from a
+	// file, if specified, or derive it from the system uuid.
+	//
+	// NB: We ignore errors here since it is better to perform the
+	// check with an empty signature than not at all.
+	var signature string
+	switch {
+	case p.Signature != "":
+		signature = p.Signature
+	case p.SignatureFile != "":
+		signature, _ = checkSignature(p.SignatureFile)
+	default:
+		signature, _ = getSystemUUID()
 	}
 
 	v := u.Query()
@@ -293,9 +294,13 @@ func checkResult(r io.Reader) (*CheckResponse, error) {
 }
 
 // getSystemUUID returns the base64 encoded, scrypt hashed contents of
-// /sys/class/dmi/id/product_uuid.
+// /sys/class/dmi/id/product_uuid, or, if that is not available,
+// sys/hypervisor/uuid.
 func getSystemUUID() (string, error) {
 	uuid, err := ioutil.ReadFile("/sys/class/dmi/id/product_uuid")
+	if os.IsNotExist(err) {
+		uuid, err = ioutil.ReadFile("/sys/hypervisor/uuid")
+	}
 	if err != nil {
 		return "", err
 	}

vendor/manifest

@@ -803,7 +803,7 @@
 		{
 			"importpath": "github.com/weaveworks/go-checkpoint",
 			"repository": "https://github.com/weaveworks/go-checkpoint",
-			"revision": "a235d5b1d2bd7be80fa52ff681f6d6baa933f635",
+			"revision": "d99cc14f13e7845b370a7dc81d47cafb29cdc97f",
 			"branch": "master"
 		},
 		{