As of the release of 7.4.1708, the official centos docker containers are
now available via multiarch support from the docker hub. For those of
you who have been using the centos/aarch64 namespaced base container,
you can now use 'FROM centos' as the proper method.

I'll keep the centos/aarch64 container around for a little while longer
to give people time to migrate.

TL;DR: 'docker pull centos' now does the right thing, and provides the
image appropriate for your architecture.