[QA] Moving to docker-pkg

[Tyler Cipriani]

Hi all,

This is a heads-up that I started transitioning CI docker images over to 
using docker-pkg[0] (which is what is used currently to build production 
images) as opposed to build.py in the integraiton/config repo. This also 
transitions things over to using docker-registry.wikimedia.org vs 
dockerhub.

I wrote up how to use docker-pkg on mw.org[1]. There is also a patch for 
a fab task that will automagically push docker images to the registry 
via contint1001 up on gerrit[2].

Thanks!

-- Tyler

[0].<https://gerrit.wikimedia.org/r/#/admin/projects/operations/docker-images/docker-pkg>
[1].<https://www.mediawiki.org/wiki/Continuous_integration/Docker#Images_using_docker-pkg>
[2].<https://gerrit.wikimedia.org/r/#/c/391592/1>