Fix circleci build step

.circleci/config.yml

@@ -17,13 +17,17 @@ jobs:
       - setup_remote_docker
       - run: |
           printf '{"commit":"%s","version":"%s","source":"https://github.com/%s/%s","build":"%s"}\n' "$CIRCLE_SHA1" "$CIRCLE_TAG" "$CIRCLE_PROJECT_USERNAME" "$CIRCLE_PROJECT_REPONAME" "$CIRCLE_BUILD_URL" > version.json
-      - run: docker build -t app:build .
+      - &build
+        run:
+          name: Build
+          command: docker build -t app:build .
 
   test:
     machine: true
     working_directory: ~/mozilla/python_mozaggregator
     steps:
       - checkout
+      - *build
       - run: docker info
       - run: docker --version
       - run: make test