[build] Skip CDN assets build when testing docker contexts (elastic#1…

…70735)

When testing docker contexts we skip all build steps related to Kibana
artifacts. CDN assets rely on the Kibana base folder and should be
skipped too.

Fixes
https://buildkite.com/elastic/kibana-artifacts-snapshot/builds/3445
Build
https://buildkite.com/elastic/kibana-artifacts-snapshot/builds/3451
Bug introduced in elastic#169707

.buildkite/scripts/steps/artifacts/docker_context.sh

@@ -11,7 +11,7 @@ KIBANA_DOCKER_CONTEXT="${KIBANA_DOCKER_CONTEXT:="default"}"
 
 echo "--- Create contexts"
 mkdir -p target
-node scripts/build --skip-initialize --skip-generic-folders --skip-platform-folders --skip-archives --docker-context-use-local-artifact
+node scripts/build --skip-initialize --skip-generic-folders --skip-platform-folders --skip-archives --skip-cdn-assets --docker-context-use-local-artifact
 
 echo "--- Setup context"
 DOCKER_BUILD_FOLDER=$(mktemp -d)