Raise error if using a non linked clone VM twice

Fix https://github.com/GNS3/gns3-gui/issues/1593

gns3server/handlers/api/compute/virtualbox_handler.py

@@ -56,7 +56,7 @@ class VirtualBoxHandler:
                                                  request.match_info["project_id"],
                                                  request.json.get("node_id"),
                                                  request.json.pop("vmname"),
-                                                 request.json.pop("linked_clone"),
+                                                 linked_clone=request.json.pop("linked_clone"),
                                                  console=request.json.get("console", None),
                                                  adapters=request.json.get("adapters", 0))
 

gns3server/handlers/api/compute/vmware_handler.py

@@ -56,7 +56,7 @@ class VMwareHandler:
                                                    request.match_info["project_id"],
                                                    request.json.get("node_id"),
                                                    request.json.pop("vmx_path"),
-                                                   request.json.pop("linked_clone"),
+                                                   linked_clone=request.json.pop("linked_clone"),
                                                    console=request.json.get("console", None))
 
         for name, value in request.json.items():