Automatic merge from submit-queue (batch tested with PRs 66196, 67016, 66807, 67023). 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>.

e2e test harness - use busybox from dockerhub

**What this PR does / why we need it**:

Use the same pattern used everywhere in the e2e test
harness, just use "busybox" (from dockerhub) instead
of using the one from k8s.gcr.io registry.

Change-Id: I700b59f73fd31f2ed6d7f995cd9441839857dd44

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```