Merge branch 'sh-allow-danger-to-fail' into 'master'

Allow Danger step to fail

See merge request gitlab-org/gitlab-ce!20624

.gitlab-ci.yml

@@ -351,6 +351,7 @@ retrieve-tests-metadata:
 danger-review:
   image: registry.gitlab.com/gitlab-org/gitaly/dangercontainer:latest
   stage: prepare
+  allow_failure: true
   before_script:
     - source scripts/utils.sh
     - retry gem install danger --no-ri --no-rdoc