Automatic merge from submit-queue

GCI/Trusty: Fix the running of kube-addon-manager

This PR fixes the issue that kube-addon-master (added in #23600) is not started. Without this fix, no kube-system pods can be running correctly. As a result, the GCI-based Jenkins testing k8s head has been down for a couple of days. The root cause is that we stopped to use namespace.yaml, but configure-helper.sh still tries to copy it. This PR also gets rid of /var/cache/kubernetes-install/kube_env.yaml, as it is not needed anymore after #24108.

@mikedanese @roberthbailey @dchen1107 please review it. If possible please mark it as P1, as it blocks GCI-based Jenkins tests.

cc/ @kubernetes/goog-image @fabioy FYI