Add CI file

.gitlab-ci.yml

+stages:
+  - build
+  - test
+  - release
+
+variables:
+  CONTAINER_TEST_IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
+  CONTAINER_RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest
+
+build-except-master:
+  stage: build
+  variables:
+    IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
+  script:
+    - docker build -t $IMAGE_TAG .
+    - docker push $IMAGE_TAG
+  only:
+    - branches
+  except:
+    - master
+
+test:
+  stage: test
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker run $CONTAINER_TEST_IMAGE /bin/sh
+
+release-image:
+  stage: release
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
+    - docker push $CONTAINER_RELEASE_IMAGE
+  only:
+    - master