Did you make sure to follow all the instructions from the README document in the Ostro OS XT GitHub site? https://github.com/ostroproject/ostro-os-xt/blob/master/README.rst.
I’ve been looking for the first set of instructions that you are running but I haven’t find them yet. I mean the first three lines from your first set of instructions. I would like to test it, but I would prefer to do it the same way you’re doing it, so if you are you using a different guide please let us know.
Also, you’re following the instructions to build the image without Docker, have you tried doing it with Docker? Is there any reason why you wouldn’t do it that way?