add gitlab ci file.

.gitlab-ci.yml

+stages:
+  - test
+  - publish
+
+test:
+  stage: test
+  image: openjdk:8
+  script:
+    - ./gradlew clean test
+
+
+.build-image:
+  stage: publish
+  image: docker:stable
+  services:
+    - docker:dind
+  script:
+    - docker login -u "$REGISTRY_USER" -p "$REGISTRY_PASSWORD" "$REGISTRY"
+    - docker build --pull -t "$IMAGE_TAG" -f "$DOCKERFILE" .
+    - docker push "$IMAGE_TAG"
+    - docker logout
+
+build-tagged-image:
+  extends: .build-image
+  variables:
+    IMAGE_TAG: "$CI_REGISTRY_IMAGE:$CI_COMMIT_TAG"
+    REGISTRY_PASSWORD: "$CI_REGISTRY_PASSWORD"
+    REGISTRY_USER: "$CI_REGISTRY_USER"
+    REGISTRY: "$CI_REGISTRY"
+    DOCKERFILE: "Dockerfile"
+  only:
+    - tags
+
+build-latest-image:
+  extends: .build-image
+  variables:
+    IMAGE_TAG: "$CI_REGISTRY_IMAGE:latest"
+    REGISTRY_PASSWORD: "$CI_REGISTRY_PASSWORD"
+    REGISTRY_USER: "$CI_REGISTRY_USER"
+    REGISTRY: "$CI_REGISTRY"
+    DOCKERFILE: "Dockerfile"
+  only:
+    - master
+
+build-feature-branch-image:
+  extends: .build-image
+  variables:
+    IMAGE_TAG: "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME"
+    REGISTRY_PASSWORD: "$CI_REGISTRY_PASSWORD"
+    REGISTRY_USER: "$CI_REGISTRY_USER"
+    REGISTRY: "$CI_REGISTRY"
+    DOCKERFILE: "Dockerfile"
+  except:
+    - master
+    - tags