Switch Docker Engine to docker-ce official repository on CentOS

Summary:
Previously, Docker was installed from two repositories:

• EPEL
• virt7, a specialized CBS on CentOS from Project Atomic.

We now switch to use the docker-ce CentOS repository from Docker.

Reference:
https://docs.docker.com/engine/installation/linux/centos/#install-using-the-repository

Test Plan:
State applied on Dwellers.

Dwellers already have this update as it was applied manually yesterday
to unstuck Mastodon containers (the docker-compose version required
Docker 1.13+, CBS still provides 1.12).

     ID: remove_legacy_docker_packages
Comment: All specified packages are already absent

     ID: install_docker_engine
Comment: All specified packages are already installed

So it's correctly, as expected no-op.

Reviewers: dereckson

Reviewed By: dereckson

Subscribers: Sandlayth

Differential Revision: https://devcentral.nasqueron.org/D987