UI: The help text for username/password while adding a node is ambiguous and not very helpful

1. Setup a cluster
2. Go to Servers tab and click on Add Servers Button
3. Notice the help text for Username and password provided.

The help text provided is ambiguous as to which username/password has to be provided ("an existing username with admin access to this server "). It's much clearer on the Old UI which says "Enter the username and password for the node you want to add to this cluster." We should make the help text unambiguous and helpful like the old UI.