Automatic merge from submit-queue

GCI/Trusty: Fix an issue in using 'find' commands

This PR makes the logic of 'find' command consistent with the 'cp' command afterwards, i.e., only check one layer of a given dir. Without this fix, we have seen a recent breakage after PR #25309 added the file cluster/addons/fluentd-elasticsearch/es-image/template-k8s-logstash.json. The 'find' command discovers this json file, but the 'cp' command fails. 

@roberthbailey @dchen1107 @zmerlynn please review this fix, and mark it as a cherry pick candidate. I already verified this fix can resolve the breakage.

cc/ @wonderfly @fabioy @kubernetes/goog-image FYI