Merge branch 'feature-ci' into 'master'

Add CI configuration

See merge request dockerfiles/steam!1

.gitlab-ci.yml

@@ -0,0 +1,34 @@
+# Official docker image for docker.
+image: docker:latest
+
+services:
+  - docker:dind
+
+before_script:
+  - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+
+stages:
+  - build
+  - deploy
+
+build-master:
+  stage: build
+  image: "docker:latest"
+  tags:
+    - dind
+  script:
+    - docker build -t "$CI_REGISTRY_IMAGE" .
+    - docker push "$CI_REGISTRY_IMAGE"
+  only:
+    - master
+
+build:
+  stage: build
+  image: "docker:latest"
+  tags:
+    - dind
+  script:
+    - docker build -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
+    - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
+  except:
+    - master