✅ Travis: Try a multi-stage build

.travis.yml

@@ -6,10 +6,21 @@ services:
 git:
   submodules: false  # Avoid trying to checkout private data/ submodule
 
-install:
+
+jobs:
+  include:
+    - stage: Build Docker image
+      script:
+        - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
         - FORCE_DOWNLOAD=y ./build
+        - docker images
+        - docker tag my_ocrd_workflow $DOCKER_USERNAME/my_ocrd_workflow
+        - docker push $DOCKER_USERNAME/my_ocrd_workflow
+    - stage: Test
+      script:
+        - docker pull $DOCKER_USERNAME/my_ocrd_workflow
+        - docker tag $DOCKER_USERNAME/my_ocrd_workflow my_ocrd_workflow
 
-script:
         - curl -O https://qurator-data.de/examples/actevedef_718448162.first-page.zip
         - unzip actevedef_718448162.first-page.zip
         - cd actevedef_718448162.first-page