Use latest docker in ruby_docker builder images

We are currently using the native docker.io package from Jessie suite in our ruby_docker image (the one we use for building GitLab and QA docker images ). This is a pretty old version and has some limitation (like, not allowing too much nesting in repo/image names, like seen in this build)

$ docker pull registry.gitlab.com/gitlab-org/omnibus-gitlab/gitlab-ce:omnibus-49384ca56c4341c976c85789882e1ba3319305e0
Invalid repository name (omnibus-gitlab/gitlab-ce), only [a-z0-9-_.] are allowed

This will break our triggered QA builds. So we should use the official docker installation documentation and hence will have latest version of docker

Sample build using an image that uses the official docker package: https://dev.gitlab.org/gitlab/omnibus-gitlab/pipelines/53165 to make sure nothing is broken.

mentioned in merge request !1674 (merged)

Closed by : https://gitlab.com/gitlab-org/gitlab-omnibus-builder/merge_requests/51

closed