Merge branch 'set-workflow-default-and-rules' into 'master'

Set 'workflow:rules', and 'default'

See merge request gitlab-org/gitlab-exporter!112

.gitlab-ci.yml

-image: "ruby:2.3"
+default:
+  image: "ruby:2.3"
+  before_script:
+    - git config --global user.email "bot@gitlab.com"
+    - git config --global user.name "Bot User"
+    - bundle install -j $(nproc) --path vendor
+  cache:
+    paths:
+      - vendor
+  tags:
+    - gitlab-org
 
-before_script:
-  - git config --global user.email "bot@gitlab.com"
-  - git config --global user.name "Bot User"
-  - bundle install -j $(nproc) --path vendor
-
-cache:
-  paths:
-    - vendor
+workflow:
+  rules:
+    # For merge requests, create a pipeline.
+    - if: '$CI_MERGE_REQUEST_IID'
+    # For `master` branch, create a pipeline (this includes on schedules, pushes, merges, etc.).
+    - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
+    # For tags, create a pipeline.
+    - if: '$CI_COMMIT_TAG'
 
 rspec:
   script: