Add release stage

.gitlab-ci.yml

 stages:
   - build
   - test
+  - release
 
 variables:
-  CONTAINER_TEST_IMAGE: boileaum/rosen:latest
+  CONTAINER_TEST_IMAGE: boileaum/rosen:$CI_COMMIT_REF_NAME
+  CONTAINER_RELEASE_IMAGE: boileaum/rosen:latest
 
 before_script:
   - echo $DOCKERHUB_PASSWD | docker login -u boileaum --password-stdin
@@ -21,7 +23,17 @@ t:docker:
   tags:
     - shell, docker
   script:
-    #- docker build --pull -t boileaum/rosen:latest -f ./docker/Dockerfile-rosen .
     - docker pull $CONTAINER_TEST_IMAGE
     - docker run $CONTAINER_TEST_IMAGE /bin/bash -c 'pytest -v'
 
+r:docker:
+  stage: release
+  tags:
+    - shell, docker
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
+    - docker push $CONTAINER_RELEASE_IMAGE
+  only:
+    - master
+