Add gitlab CI template

.gitlab-ci.yml

+# This file is a template, and might need editing before it works on your project.
+docker-build-master:
+  # Official docker image.
+  image: docker:latest
+  stage: build
+  services:
+    - docker:dind
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+  script:
+    - docker build --pull -t "$CI_REGISTRY_IMAGE" .
+    - docker push "$CI_REGISTRY_IMAGE"
+  only:
+    - master
+
+docker-build:
+  # Official docker image.
+  image: docker:latest
+  stage: build
+  services:
+    - docker:dind
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+  script:
+    - docker build --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
+    - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
+  except:
+    - master