New base image needed

[zeldin]

The base image ubuntu:17.10 can no longer be used. Ubuntu removed all the package files, so apt-get won't work.
We could upgrade to ubuntu:18.04, which is LTS, or take the opportunity to switch to Debian, which supports more architectures, by picking e.g. debian:9-slim. The Debian slim base image is also smaller in size, although the difference in size of the final image is rather small if you look at it as a percentage of the whole size. 😄

Base image	Base image size	ps3dev-docker image size
ubuntu:18.04	69.9MB	1.88GB
debian:9-slim	55.3MB	1.84GB