Refactor CI to support multiple docker images

.gitlab-ci.yml

-docker-build-master:
+.docker-build_template: &build_template
   # Official docker image.
   image: docker:latest
   stage: build
@@ -6,22 +6,9 @@ docker-build-master:
     - 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" $CI_REGISTRY
+build:project-usage-to-influx:
+  <<: *build_template
   script:
-    - docker build --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
+    - docker build --pull -t "${CI_REGISTRY_IMAGE}-project-usage-to-influx:$CI_COMMIT_REF_SLUG" ./project-usage-to-influx/
     - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
-  except:
-    - master