Don't show errors not related to a user role to the user

1. Create a cluster query and index nodes with bucket and data in it.
2. Create an user with non-admin/non-cluster role assigned to it (ex: Query Select role).
3. Login to the cluster with the above user. Also parallely log into the admin user on a different browser
4. Start a rebalance by adding a node into the cluster by an admin and fail the rebalance by killing the ns_server on the added node. We see an error saying "Rebalance failed. See logs for detailed reason. You can try again." on both the browsers 

The non-admin/non-cluster admin should not see such errors since he cannot act on the errors nor can he see the logs. We should shield user from unwanted information such as above. And in any case the Admin responsible for the rebalance does get notified and can act on the error.