The line `hosts: UbuntuTest` is telling ansible that it should look into your inventory for a group (or a host) named UbuntuTest. The error you are getting is indicating that you have no such group or host within your inventory.
My recommendation would be to double check your awx inventory tied to your job template to see if has a group or host with that name. If not, add one and try again and see if it works.
Also, I would recommend changing your playbook to say `hosts: all` and then set a limit in the job template inside AWX. That way, if you wanted to have multiple job templates that pointed to different hosts they could all use the same playbook (applying the limit from the job template itself).
-John