Bake docker-ce into the base image

Speeds up CI runs by quite a bit

.circleci/base-image/build.bash

@@ -0,0 +1,15 @@
+#!/bin/bash
+set -euo pipefail
+
+# Very simple script to build and push images
+# Should be replaced by chartpress or similar at some point
+# Uses google container image builder for simplicity
+IMAGE="jupyterhub/tljh-circleci-base-image"
+TAG=$(git log -n1 --pretty="%h" .)
+IMAGE_SPEC="${IMAGE}:${TAG}"
+
+
+echo "Building and pushing ${IMAGE_SPEC}"
+docker build -t ${IMAGE_SPEC} .
+docker push ${IMAGE_SPEC}
+echo "Built and pushed ${IMAGE_SPEC}"