Make the creation of Docker images a specific process to ask in Gitlab interface

This MR aims to address #16 (closed) .

As usual @steff and @vicente.mataix your input is welcome!

.gitlab-ci.yml

@@ -7,22 +7,24 @@ build_docker:
     stage: build
     retry: 2
     only:
-        refs:
-            - master
+        - web
     script:
         - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
-        - docker build -f docker/Dockerfile -t $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling:latest .
+        # Latest is always generated but not pushed if ${UPDATE_LATEST_TAG} is not "True"
+        - docker build -f docker/Dockerfile -t $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling:${TAG} -t $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling:latest .
         - docker container prune
-        - docker push $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling:latest
+        - docker push $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling:${TAG}
+        - if [ "${UPDATE_LATEST_TAG}" == "True" ]; then docker push $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling:latest; fi
 
 build_docker_full:
     stage: build
     retry: 2
     only:
-        refs:
-            - master
+        - web
     script:
         - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
-        - docker build -f docker/Dockerfile_full -t $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling-and-compilers:latest .
+        # Latest is always generated but not pushed if ${UPDATE_LATEST_TAG} is not "True"
+        - docker build -f docker/Dockerfile_full -t $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling-and-compilers:${TAG} -t $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling-and-compilers:latest .
         - docker container prune
-        - docker push $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling-and-compilers:latest
\ No newline at end of file
+        - docker push $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling-and-compilers:${TAG}
+        - if [ "${UPDATE_LATEST_TAG}" == "True" ]; then docker push $CI_REGISTRY/$CI_PROJECT_PATH/xeus-cling-and-compilers:latest; fi
\ No newline at end of file