The docker toolchain is a bit of a walled garden and speculative image
builds work great by default as long as docker.io is your image
registry. As soon as you start trying to host images elsewhere it
becomes a lot more complicated to use speculatively built images during
docker image builds.
Update our existing registry role test jobs to use images hosted
somewhere other than docker.io to force us onto the less happy code
path, then verify that we are able to build images from speculative
states using docker. This should give us decent coverage that everything
works as expected.
Change-Id: I4801f98a0ef1aab01b4bc3b6e6576800efacbac4
5dcc397840