I've been able to install 4.0beta in Bionic as well, no issues so far.
But that sentence in your original post:
>it complains that the oxauth.war file is missing and looking in the directory /opt/dist/gluu/oxauth.war
>it should look into the install directory, which is /opt/gluu-server/opt/dist/gluu/oxauth.war
looks a bit strange to me. Actually, the path `/opt/dist/gluu/oxauth.war` is correct, as `setup.py` is run from inside the container, so all paths will be relative to its root. The fact that you expect it to be relative to `/opt/gluu-server/` made me wonder whether you actually enter container before running it.
Please note that this step - `# /sbin/gluu-serverd-4.0 login` - is mandatory, prior to running the script.
If this is not the case and you are able to enter the container, please provide us all log files this command will return: `# ls /install/community-edition-setup/*.log`
Also, please follow Sahil's suggestion and share with us a step-by-step of your actions, and the full list of options you select when running `setup.py` (just save all output it displays when you run it).