Merge branch 'jprovazn-rails-ci' into 'master'

Trigger rails5 tests if variable is set

See merge request gitlab-org/gitlab-ce!20609

.gitlab-ci.yml

@@ -86,7 +86,9 @@ stages:
 .rails5: &rails5
   allow_failure: true
   only:
-    - /rails5/
+    variables:
+      - $CI_COMMIT_REF_NAME =~ /rails5/
+      - $RAILS5_ENABLED
   variables:
     BUNDLE_GEMFILE: "Gemfile.rails5"
     RAILS5: "true"