feat: nodeup will only check the nodeupConfigHash if it is provided

On bare metal, the nodeupConfig is harder to predict and we will have
to use other ways to trigger an update anyway.

upup/pkg/fi/nodeup/command.go

@@ -154,8 +154,10 @@ func (c *NodeUpCommand) Run(out io.Writer) error {
 		return fmt.Errorf("no instance group defined in nodeup config")
 	}
 
-	if want, got := bootConfig.NodeupConfigHash, base64.StdEncoding.EncodeToString(nodeupConfigHash[:]); got != want {
-		return fmt.Errorf("nodeup config hash mismatch (was %q, expected %q)", got, want)
+	if want := bootConfig.NodeupConfigHash; want != "" {
+		if got := base64.StdEncoding.EncodeToString(nodeupConfigHash[:]); got != want {
+			return fmt.Errorf("nodeup config hash mismatch (was %q, expected %q)", got, want)
+		}
 	}
 
 	err = evaluateSpec(&nodeupConfig, bootConfig.CloudProvider)