gitlab: Upload images to dockerhub

It can be convenient to upload images to dockerhub for redundancy and
visibility, so this patch updates the gitlab CI configuration to do
that.

While at it, rename the stages for readability.

.gitlab-ci.yml

@@ -1,10 +1,10 @@
 
 stages:
   - test
-  - docker_image
+  - image
 
 # Integration test, using the module versions from the repository.
-integration_test:
+stable:
   stage: test
   image: docker:stable
   services:
@@ -16,7 +16,7 @@ integration_test:
     - docker run chasquid-test  make test
 
 # Integration test, using the latest module versions.
-integration_test_latest:
+latest:
   stage: test
   image: docker:stable
   services:
@@ -27,8 +27,9 @@ integration_test_latest:
     - docker run chasquid-test  env
     - docker run chasquid-test  make test
 
-image_build:
-  stage: docker_image
+# Build docker image, upload to gitlab registry.
+build_gitlab:
+  stage: image
   image: docker:stable
   services:
     - docker:dind
@@ -37,3 +38,15 @@ image_build:
     - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
     - docker build -t $CI_REGISTRY_IMAGE:$CI_BUILD_REF_NAME -f docker/Dockerfile .
     - docker push $CI_REGISTRY_IMAGE:$CI_BUILD_REF_NAME
+
+# Build docker image, upload to dockerhub registry.
+build_dockerhub:
+  stage: image
+  image: docker:stable
+  services:
+    - docker:dind
+  script:
+    - docker info
+    - docker login -u $DOCKER_REGISTRY_USER -p $DOCKER_REGISTRY_PASSWORD docker.io
+    - docker build -t index.docker.io/albertito/chasquid:$CI_BUILD_REF_NAME -f docker/Dockerfile .
+    - docker push index.docker.io/albertito/chasquid:$CI_BUILD_REF_NAME