GUACAMOLE-292: Restrict attributes on object management pages to those explicitly present on the object.

guacamole/src/main/webapp/app/manage/templates/manageUser.html

@@ -41,7 +41,8 @@
 
         <!-- User attributes section -->
         <div class="attributes" ng-show="canChangeAttributes()">
-            <guac-form namespace="'USER_ATTRIBUTES'" content="attributes" model="user.attributes"></guac-form>
+            <guac-form namespace="'USER_ATTRIBUTES'" content="attributes"
+                       model="user.attributes" model-only="true"></guac-form>
         </div>
 
         <!-- System permissions section -->