Finally I found the root cause which is my mistake and a miss-implemented UI in create cluster form !
I am entering wrong IP addresses in the form;s VIPs being the same as the demo node ones and they must be different IPs for MVVIP and SVIP. So I need to enter 2 IPs for each Management ans storage interfaces, one for the node's IP and a second for Virtual IP. It is something that easily can implemented in the create cluster html form to report this error which isn't showing.
I entered the following HTML block in the create cluster form html code in order to see the actual error :
Also it may be good to add a note on the demo instructions.