Automatic merge from submit-queue

Trusty: Handle the new var in kube-proxy manifest

This is to capture the kube-proxy manifest change in PR #24429.

@roberthbailey @fabioy @zmerlynn please review this change and mark it as cherry pick candidate. We need to catch up 1.2.3 release.

cc/ @dchen1107 @wonderfly @cjcullen FYI.

I have verified this fix. Without this fix, kube-proxy pod in Trusty nodes cannot be started correctly, i.e., the command line has an unhadled variable. And some other kube-system pods do not work correctly as kube-proxy is not working well. After applying this fix, kube-proxy can be started correctly, and all kube-system pods run successfully.