Since we have switched from debian to ubuntu based image and changed the
name (in https://review.opendev.org/733078) we need to align it with
airshipctl repository.
Renaming the following names:
1) debian-custom.iso -> ubuntu-focal.iso
2) quay.io/airshipit/isogen:latest-debian_stable -> quay.io/airshipit/isogen:latest-ubuntu_focal
Updating the following packages and resources:
1) k8s 1.17.3 -> 1.18.6
2) docker 19.03.9 -> 19.03.12
3) Calico 3.9 -> 3.15
Change-Id: I7eaf382acb79016a511db6e0955fa932c02963c4
582894d389