Merge branch 'use-git-depth-1-on-cng-trigger' into 'master'

Set GIT_DEPTH to 1 to speed up cloning for the cloud images trigger

See merge request gitlab-org/gitlab-ce!19098

.gitlab-ci.yml

@@ -307,6 +307,8 @@ cloud-native-image:
   before_script: []
   stage: build
   allow_failure: true
+  variables:
+    GIT_DEPTH: "1"
   cache: {}
   before_script:
     - gem install gitlab --no-rdoc --no-ri