minion: Upgrade Docker Engine to 1.12.3
minion: Upgrade Docker Engine to 1.12.3

The Docker daemon has been hanging randomly when running the Spark
integration test. We theorize that this is fixed by
https://github.com/docker/libnetwork/pull/1507, which was released in
Docker 1.12.3.

LuiseV/quilt,LuiseV/quilt,PenguinToast/quilt,PenguinToast/quilt,NetSys/quilt,NetSys/quilt,mmussomele/quilt,tejasmanohar/quilt,stevenlin598/quilt,stevenlin598/quilt,ejj/quilt-dev,kklin/quilt,mmussomele/quilt,LuiseV/quilt,kklin/quilt,PenguinToast/quilt,kelda/kelda,stevenlin598/quilt,quilt/quilt,ejj/quilt-dev,kklin/kelda,stevenlin598/quilt,quilt/quilt,NetSys/quilt,PenguinToast/quilt,kelda/kelda,tejasmanohar/quilt,stevenlin598/quilt,mmussomele/quilt,kklin/kelda,NetSys/quilt,kayousterhout/quilt,tejasmanohar/quilt,ejj/quilt-dev,PenguinToast/quilt,quilt/quilt,tejasmanohar/quilt,kklin/kelda,ejj/quilt-dev,kayousterhout/quilt,LuiseV/quilt,kelda/kelda,mmussomele/quilt,mmussomele/quilt,kklin/quilt,kklin/quilt,kayousterhout/quilt,kelda/kelda,LuiseV/quilt,stevenlin598/quilt,kklin/kelda,NetSys/quilt,kayousterhout/quilt,quilt/quilt,mmussomele/quilt