Automatic merge from submit-queue (batch tested with PRs 55283, 55461, 55288, 53970, 55487). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>. Add more comments for DevicePluginHandlerImpl struct **What this PR does / why we need it**: Add more comments **Special notes for your reviewer**: @jiayingz PTAL. **Release note**: ``` NONE ```