Automatic merge from submit-queue
Fix hack/update-api-reference-docs on master and (future) branches
- update toplevel api object pattern in swagger doc script: the format of the `register.go` file was changed in e3af3451c8. This fixes the bleeding.
- make `hack/update-api-reference-docs.sh` independent from master during **container run**. Container build is still dependent on master, but container rebuilds never happen I guess on a branch.
A rebuild of `gcr.io/google_containers/gen-swagger-docs:v6` is necessary, plus a cherry-pick onto the v1.3 branch.
Fixes the symptoms of #27685 and makes sure future branches do not break again.