I think it's better to stick with CentOS7 or Ubuntu 16 for now; as 4.0 CB is not even in beta state...
Also.. I would use IP address of VM in `Couchbase host` value.
Another off topic question, have you tested your SSO functionality with Gluu Server yet?
If not then I would first check that with stable version of Gluu Server, i.e. 3.1.6.
Afterwards, you can migrate your config to Gluu 4.0 when it's released properly.